THE  ORIGIN  OF  THE  EARTH 


THE  UNIVERSITY  OF  CHICAGO  PRESS 
CHICAGO,  ILLINOIS 


THE  BAKER  &  TAYLOR  COMPANY 

NEW  YOBK 

THE  CUNNINGHAM,  CURTISS  &  WELCH  COMPANY 

LOS  ANGELES 


THE  CAMBRIDGE  UNIVERSITY  PRESS 

LONDON  AND  EDINBURGH 

THE  MARUZEN-KABUSHIKI-KAISHA 

TOKYO,  OSAKA,   KYOTO 

THE  MISSION  BOOK  COMPANY 

SHANGHAI 


KARL  W.  HIERSEMANN 


THE.ORIGIN  OF  THE 
EARTH  » 


By 

THOMAS  CHROWDER  CHAMBERLIN 

Head  of  the  Department  of  Geology 
The  University  of  Chicago 


THE  UNIVERSITY  OF  CHICAGO  PRESS 
CHICAGO,  ILLINOIS 


COPYRIGHT  igi6  By 
THE  UNIVERSITY  or  CHICAGO 


All  Rights  Reserved 


Published  June  1916 


Composed  and  Printed  By 

The  University  of  Chicago  Press 

Chicago,  Illinois,  U.S.A. 


TO 

TWO  AMERICANS, 

AMONG  PATRONS   OF   SCIENCE  AND  EDUCATION 
THE   MOST   GENEROUS, 
AMONG  PHILANTHROPISTS 

THE   MOST  WISE, 
THIS   LITTLE    OFFSPRING   OF   THEIR   GIFTS 

IS 
DEDICATED 


336085 


THE  UNIVERSITY  OF  CHICAGO 
SCIENCE  SERIES 


Editorial  Committee 
ELIAKIM   HASTINGS  MOORE,  Chairman 

JOHN  MERLE  COULTER 
ROBERT  ANDREWS  MILLIKAN 


The  University  of  Chicago  Science  Series, 
established  by  the  Trustees  of  the  University, 
owes  its  origin  to  a  feeling  that  there  should 
be  a  medium  of  publication  occupying  a 
position  between  the  technical  journals  with 
their  short  articles  and  the  elaborate  treatises 
which  attempt  to  cover  several  or  all  aspects 
of  a  wide  field.  The  volumes  of  the  series 
will  differ  from  the  discussions  generally 
appearing  in  technical  journals  in  that  they 
will  present  the  complete  results  of  an  experi- 
ment or  series  of  investigations  which  previ- 
ously have  appeared  only  in  scattered  articles, 
if  published  at  all.  On  the  other  hand,  they 
will  differ  from  detailed  treatises  by  confining 
themselves  to  specific  problems  of  current 
interest,  and  in  presenting  the  subject  in  as 
summary  a  manner  and  with  as  little  technical 
detail  as  is  consistent  with  sound  method. 
They  will  be  written  not  only  for  the  specialist 
but  for  the  educated  layman. 


PREFACE 

In  telling  the  story  of  this  search  for  the  mode  by 
which  the  earth  came  into  being,  we  have  let  the  inci- 
dents that  led  the  inquiry  on  from  one  stage  to  another 
fall  in  with  the  steps  of  the  inquiry  itself.  It  is  in 
keeping  with  the  purposes  of  this  series  of  booklets  that 
the  motives  which  set  researches  a-going  should  have 
their  place  with  the  quests  that  arose  from  them.  At 
any  rate,  it  is  clear  that  the  reader  will  be  at  some 
advantage  in  forming  his  own  judgment  of  the  value  of 
what  is  offered  for  his  acceptance,  if  the  lines  along 
which  the  inquiry  was  approached,  the  conditions 
that  affected  the  mental  attitude  of  the  inquirer,  and 
the  considerations  that  weighed  in  reaching  conclusions 
are  laid  as  frankly  before  him  as  the  conclusions  them- 
selves. 

The  reader  will  of  course  choose  his  own  pace,  but 
it  were  well  if  it  were  deliberate.  •  Pictures  of  nebulae 
and  nebulous  pictures  rise  slowly  into  good  definition. 
Besides,  the  interpretations  we  offer  are  tentative; 
it  were  well  to  detain  them  a  little  for  scrutiny  as  they 
pass  under  review.  The  final  story  of  the  birth  of  the 
earth  will  come  only  after  a  time  when  the  vestiges  of 
creation  have  been  more  keenly  discerned  and  more 
faithfully  rendered  than  is  possible  now. 

And  yet  one  may  indulge  the  belief  that,  in  due  time 
and  with  adequate  patience,  the  earliest  history  of  the 
earth  may  be  deciphered  with  a  confidence  not  unlike 
that  we  now  repose  in  the  interpretation  of  its  strati- 
graphic  pages. 


IX 


x  PREFACE 

The  reader  will  appreciate  the  kindness  of  the  Direc- 
tors of  the  Lick,  the  Yerkes,  and  the  Mount  Wilson 
observatories  in  permitting  free  use  of  their  photo- 
graphic material  for  illustrations.  I  am  under  great 
obligations  to  Professors  F.  R.  Moulton,  H.  N.  McCoy, 
and  R.  T.  Chamberlin  for  reading  my  manuscript,  in 
whole  or  in  part,  and  for  critical  suggestions  that  have 
been  very  helpful.  Throughout  the  whole  of  the  cos- 
mogonic  studies,  ranging  backward  through  two  decades, 
of  which  this  little  booklet  is  the  outcome,  I  have  been 
a  debtor  in  a  peculiar  degree  to  Dr.  Moulton  for  aid, 
advice,  and  co-operation  in  various  inquiries  involving 
celestial  mechanics  and  kindred  applications  of  the 
higher  resources  of  mathematics.  This  assistance  has 
been  nothing  less  than  indispensable. 

T.  C.  C. 


CONTENTS 

PAGE 

INTRODUCTION ..    .     *     .     .     .         i 

CHAPTER 

I.  THE  GASEOUS  THEORY  or  EARTH-GENESIS  IN  THE 
LIGHT  OF  THE  KINETIC  THEORY  or  GASES        .     .       10 

II.  VESTIGES  OF  COSMOGONIC  STATES  AND  THEIR  SIG- 
NIFICANCE   38 

III.  THE  DECISIVE  TESTIMONY  OF  CERTAIN  VESTIGES 

OF  THE  SOLAR  SYSTEM 48 

IV.  FUTILE  EFFORTS  .     .  ^>  .     ..".     ....     .       72 

V.  THE  FORBIDDEN  FIELD  .     .     ...    l.     ...      90 

VI.  DYNAMIC  ENCOUNTER  BY  CLOSE  APPROACH  .     .     .     101 

VII.  THE  EVOLUTION  OF  THE  SOLAR  NEBULA  INTO  THE 

PLANETARY  SYSTEM 130 

VIII.  THE  JUVENILE  SHAPING  OF  THE  EARTH  ....     159 
IX.  INNER  REORGANIZATION  OF  THE  JUVENILE  EARTH    .     226 

X.  HIGHER   ORGANIZATION    IN    THE    GREAT   CONTACT 
HORIZONS 241 


XI 


INTRODUCTION 

If  it  shall  seem  strange  to  anyone  that  a  student  of  the 
story  of  the  rocks  should  turn  aside  from  a  field  so  solid 
and  congenial  to  venture  wantonly  into  the  nebulous 
wilds  of  cosmogony,  I  can  only  plead  in  defense  the 
urgent  necessities  of  the  scientific  chase.  It  came  to  be 
clear  that  only  by  close  pursuit  along  the  trail  that  led 
into  the  cosmogonic  fens  and  fogs  was  there  any  hope  of 
overhauling  the  quarry  that  had  awakened  my  instincts 
of  pursuit — a  pack  of  sophistical  sprites  that  had  long 
been  wont  to  vex  a  pet  climatic  enigma  on  whose  solution 
I  had  set  fond  hopes.  It  may  be  some  little  further 
extenuation  of  my  temerity  to  plead  that,  at  the  out- 
set, the  trail  was  picked  up  and  the  chase  begun  almost 
as  far  away  as  possible  from  the  pass  that  led  into  the 
bogs  and  mists,  and  that  at  the  start  the  trail  was  as 
cold  as  a  glacier. 

My  early  geologic  work  happened  to  fall  in  a  tract  that 
was  overlain  by  a  thick  mantle  of  glacial  drift  and 
underlain ,  by  the  sheeted  sediments  of  the  Paleozoic 
sea.s.  Above,  there  was  little  but  the  products  of  the 
strange  ice  invasion;  below,  there  was  little  within 
reach  but  the  products  of  the  ancient  seas.  Coral  reefs 
and  crinoid  fields  contested  with  moraines  and  drumlins 
the  place  of  first  affection.  Early  bias  favored  the 
sea  life,  but  the  glacial  beds  were  uppermost  in  the  field 
and  soon  came  to  be  foremost  in  the  zest  of  inquiry. 
How  ice  sheets  could  have  crept  so  far  south  upon  the 


2          t-         ..THE  ORIGIN  OF  THE  EARTH 

low  plains  in  the  heart  of  our  continent  grew  to  be  a  more 
and  more  insistent  puzzle  as  the  verity  of  the  invasion 
grew  more  and  more  incontestable.  There  were  indeed 
inherited  theories,  but  when  these  were  brought  to  test 
by  the  precise  realities  of  the  record  as  it  was  met  from 
day  to  day  in  the  field,  they  seemed  to  limp  under  the 
burden  of  explanation  they  had  taken  upon  themselves, 
and  so,  one  after  another,  they  were  turned  out  to 
pasture  as  lame  horses  no  longer  fit  to  be  ridden.  New 
theories  were  sought  in  their  place  and  ridden  as  far  as 
they  would  go.  Among  the  rest,  an  old  suggestion 
of  TyndalPs  was  saddled  up  and  mounted  with  little 
thought  of  the  outcome,  and  this  proved  to  be  the 
mount  that  was  to  carry  me  into  the  fens  and  fogs  of 
cosmogony. 

Tyndall  had  found,  in  the  course  of  his  physical 
researches,  that  carbon  dioxide  was  an  efficient  absorber 
of  heat,  and  so  he  had  entertained  the  suggestion  that  a 
deficiency  of  this  gas  in  the  atmosphere  might  be  the 
cause  of  the  low  temperatures  that  gave  rise  to  the  ice 
sheets.  The  suggestion  had  been  made  so  long  before 
my  day  that  it  had  been  well-nigh  forgotten.  The 
probabilities  seemed  all  against  its  tenability.  Tyndall 
had  neglected  to  point  out  any  natural  process  by  which 
such  a  former  deficiency  in  carbon  dioxide  could  have 
arisen,  and  had  thus  left  the  theory  without  a  working 
basis;  still,  as  a  physicist,  merely  throwing  out  a  sug- 
gestion incidental  to  the  main  line  of  his  study  he  had 
done  all  that  could  fairly  be  required  of  him.  The 
history  of  the  atmosphere,  as  then  currently  interpreted, 
looked  quite  the  other  way.  It  was  generally  held,  in 
accordance  with  Laplace's  beautiful  theory  of  the  origin 


INTRODUCTION  3 

of  the  solar  system,  that  the  earth  was  at  first  all  gas — 
all  atmosphere  as  Laplace  put  it — and  that  all  the 
carbon  later  locked  up  in  the  coals,  the  oils,  the  carbona- 
ceous shales,  the  limestones,  and  the  other  carbonates 
was  then  free  gas  and  diffused  throughout  this  great 
globe  of  gas.  It  was  held  that  later,  when  cooling  had 
made  some  progress,  the  refractory  matter  that  was 
soon  to  form  the  rocks  gathered  into  a  white  hot  globe 
of  lava,  but  that  still  all  the  oxides  of  carbon  and  all 
the  water  remained  in  the  hot  atmosphere  and  gave  it 
enormous  extent  and  density.  It  was  reasoned  that 
later,  as  cooling  proceeded,  the  waters  must  have  been 
gathered  gradually  to  the  earth,  but  that  the  carbon 
dioxide  still  persisted  in  the  atmosphere  until  slowly, 
as  the  ages  went  on,  it  entered  into  union  with  the  rock 
crust  to  form  carbonates,  or  was  extracted  from  the 
air  by  plants  to  form  coals  and  other  carbonaceous 
deposits.  And  so,  each  earlier  age  was  thought  to  have 
held  more  carbon  dioxide  in  its  atmosphere  than  the 
succeeding  ones.  If  this  were  true,  it  seemed  idle  to 
go  backward  in  time  to  find  deficiency  in  carbon  dioxide. 
Besides  this  infelicity,  there  seemed  to  be  in  this  very 
fact  of  a  great  decline  from  the  very  hot  to  the  cold  a 
basis  for  a  plausible  hypothesis  of  glaciation — the  simple, 
natural  trend  of  a  moribund  earth  toward  a  cold  senility. 
The  sun  was  growing  cooler  and  less  heat  came  to  the 
earth;  the  earth-body  was  growing  colder  and  was 
shrinking  and  cracking  and  drinking  in  the  water  on  its 
surface;  the  carbon  dioxide,  oxygen,  and  other  elements 
of  the  air  were  being  drawn  in  also  and  were  uniting 
with  the  rocks,  and  so  they  blanketed  the  earth  less  and 
less  effectually;  less  moisture  rose  into  this  thinned  cold 


4  THE  ORIGIN  OF  THE  EARTH 

atmosphere  and  so  there  was  less  blanketing  by  vapor, 
and  even  when  it  rose,  the  vapor  was  more  promptly  con- 
densed to  cloud  or  floating  frost,  and  in  this  form  cut  off 
and  reflected  away  the  sunlight.  So  it  was  said  that 
the  earth  was  cooling  off  and  drying  up,  that  glaciers 
and  deserts  were  increasing,  and  that  a  final  desicca- 
tion and  a  final  winter  were  coming  events  of  the  near 
geologic  future.  We  were  told  how  the  moon  had  lost 
its  seas  (behold  the  Mare!}  and  how  its  atmosphere 
had  been  absorbed;  and  then  the  moon  was  brought  into 
court  as  a  witness  to  the  impending  fate  of  the  earth. 
Our  recent  icy  stage  was  but  an  October  frost;  December 
was  yet  to  come.  Such  was  the  picture,  and,  granting 
the  cosmogonic  views  then  current,  such  was  the  logical 
drama  foreshadowed  by  the  earth's  great  decline  from  a 
hot  beginning  toward  a  cold  end.  "The  final  winter," 
"the  universal  desert/'  "the  last  man,"  were  moving 
themes,  and  there  was  much  fine  writing — albeit  of  a 
gruesome  sort — by  those  who  delight  in  such  things. 

But  this  theory  of  a  simple  decline  from  a  fiery 
origin  to  a  frigid  end,  from  a  thick  blanket  of  warm  air  to 
a  thin  sheet  of  cold  nitrogen,  consonant  with  the  current 
cosmogony  as  it  was,  logical  under  the  premises  postu- 
lated, pessimistically  attractive  in  its  gruesome  forecast, 
already  in  possession  of  the  stage,  with  a  good  prospect 
of  holding  it — this  theory  of  a  stupendous  descensus 
none  the  less  encountered  some  ugly  facts  as  inquiry 
went  on.  It  seemed  to  accord  well  enough  with  an 
ice  age,  if  the  ice  age  came  only  in  the  later  stages  of  the 
earth's  history,  but  it  was  ill  suited  to  explain  an  ice 
age  in  the  earlier  geologic  eras.  Unfortunately  for 
it,  there  began  to  appear  signs  of  ice  ages  far  back  in 


INTRODUCTION  5 

time,  and,  besides,  some  of  these  had  their  seats  much 
nearer  the  equator  and,  in  other  respects,  were  even 
stranger  than  the  latest  great  glaciation.  The  evidence 
of  these  earlier  and  stranger  glaciations  was  at  first 
quite  naturally  received  with  incredulity,  but  the  proof 
grew  steadily  stronger  with  every  new  test,  and  the 
range  of  the  evidence  was  found  wider  and  clearer  as 
exploration  advanced.  While  all  this  should  have 
weakened,  and  did  weaken,  the  fundamental  concept 
of  great  warmth  and  a  rich  atmosphere  in  the 
earlier  ages,  while  it  should  have  roused  skepticism  as  to 
the  verity  of  the  cosmogony  on  which  it  was  based,  and 
perhaps  did  so,  still  the  old  thermal  concept  and  the 
old  cosmogony  continued  to  hamper  all  attempts  at  a 
radical  revision  of  glacial  theories.  The  old  ideas  served 
as  a  handicap  to  the  suggestion  of  Tyndall  perhaps 
more  than  most  other  attempts  at  an  explanation  of  an 
ice  age. 

None  the  less,  it  seemed  to  me  worth  while  to  inquire 
what  might  be  the  possible  climatic  effects  of  secular 
variations  in  the  constituents  of  the  atmosphere,  not 
merely  such  changes  in  the  carbon  dioxide  as  Tyndall 
had  suggested,  but  whatever  changes  had  taken  place 
in  any  of  the  constituents,  not  the  least  among  these 
the  variations  in  water-vapor,  the  factor  that  comes  and 
goes  with  a  peculiar  freedom  of  its  own.  Back  of 
this  search  for  variations,  it  was  of  course  important  to 
inquire  what  agencies  could  cause  such  variations. 

It  was  not  long  before  a  plausible  reason  for  variation 
in  carbon  dioxide  was  found.  In  a  study  of  the  deforma- 
tions of  the  crust  of  the  earth,  attention  was  soon  centered 
on  the  evidence  that  stresses  had  arisen  within  the  body 


6  THE  ORIGIN  OF  THE  EARTH 

of  the  earth  as  time  went  on  and  had  gathered  in  force 
so  long  as  the  crust  had  been  able  to  withstand  them, 
but  that,  when  resistance  was  no  longer  possible,  the 
crust  had  yielded,  and  had  become  crumpled  and  folded 
into  mountains,  or  bowed  up  into  great  swells,  or  warped 
up  into  plateaus.  There  was  naturally  much  riving, 
Assuring,  and  crushing  of  the  rock  in  the  course  of  these 
processes.  Back  of  these  there  seemed  also  to  be 
grander  movements  by  which  areas  of  continental 
magnitude  were  lifted,  while  areas  of  oceanic  extent 
were  depressed.  The  waters  were  thus  drawn  more 
deeply  into  the  great  basins  while  the  continents  stood 
more  boldly  forth.  In  these  various  ways,  wider  and 
fresher  contacts  of  the  air  with  the  rocks  arose  after 
each  of  these  episodes  of  readjustment  and  the  active 
constituents  of  the  air  entered  into  combination  with 
the  rocks  at  accelerated  rates. 

But  when  the  stresses  of  the  crust  had  been  eased  by 
these  episodes  of  warping,  folding,  and  faulting,  a  long 
epoch  of  crustal  quiet  ensued  awaiting  another  such 
growth  of  stresses  into  strength  enough  to  force  a  new 
episode  of  disruption.  During  such  long  epochs  of 
quiescence,  the  rugosities  of  the  surface  were  worn  down 
by  the  elements,  in  a  greater  or  less  measure,  and  the 
debris  was  carried  into  the  oceans  where  it  displaced  an 
equal  volume  of  water  and,  by  so  much,  lifted  the  sea- 
level.  So,  too,  all  this  time  the  sea  was  gnawing  steadily 
at  the  borders  of  the  land  and  creeping  out  upon  it.  In 
doing  this,  it  was  aided  by  the  lifting  of  the  breaker 
zone — its  cutting  edge — by  the  deposit  of  sediments  on  its 
bottom.  A  study  of  the  stratigraphic  record  showed 
that,  at  times,  a  third  or  a  half  of  the  continental  plat- 


INTRODUCTION  7 

forms  were  covered  by  the  overlapping  of  the  sea  and  the 
action  of  the  air  upon  the  rocks  was  thus  shut  off.  At 
the  same  time,  the  lands  that  were  not  thus  covered 
by  the  sea  had  been  brought  low,  in  some  large  measure, 
by  erosion,  and  became  covered  by  a  deep  mantle  of  soil 
and  residual  clay,  and  hence  suffered  a  notably  lessened 
effect  from  the  action  of  the  air.  Such  epochs  of  base 
leveling  were  therefore  clearly  times  of  very  slow  deple- 
tion of  the  atmosphere. 

Here  then  was  a  natural  process  of  a  large  order 
by  virtue  of  which  the  air  was  robbed  of  its  active  ele- 
ments in  one  set  of  stages  at  a  relatively  fast  rate,  while 
in  the  other  set  of  stages  at  only  a  relatively  slow  rate. 
The  cause  of  the  fast  action  was,  if  a  technical  term 
may  be  pardoned,  diastrophism ;  the  cause  of  the  slow 
action  was  planation.  Each  stage  occupied  a  long  time, 
but  the  periods  of  planation  were  much  longer  than  the 
episodes  of  diastrophism. 

The  recognition  of  this  alternation  of  rapid  atmos- 
pheric depletion  with  slow  atmospheric  depletion  gave 
a  pulsatory  aspect  to  the  atmospheric  history.  When, 
in  addition  to  this,  it  was  recognized  that  the  earth 
through  its  volcanoes  had  all  along  been  feeding  the 
atmosphere  as  well  as  feeding  upon  it,  and  that  this 
feeding  was  also  pulsatory,  the  case  took  on  troublesome 
complications,  and  a  more  severe  scrutiny  of  the  strati- 
graphic  record,  and  of  the  relics  of  life  imbedded  in  it, 
became  imperative.  In  the  course  of  this,  still  further 
departures  from  the  generalizations  of  the  inherited 
view  came  to  notice.  Desiccation  products  were  found 
to  be  scarcely  less  abundant  and  characteristic  in  the 
early  strata  than  in  the  later,  and  no  steady  progress 


8  THE  ORIGIN  OF  THE  EARTH 

from  humidity  to  aridity  seemed  to  mark  the  progress 
of  time;  nor  were  there  found  any  conclusive  evidences 
of  even  an  oscillatory  progress  from  predominant  humid- 
ity to  predominant  aridity.  If  the  record  favored  any 
generalization,  it  seemed  to  be  that  the  severest  and  most 
prevalent  period  of  aridity  fell  near  the  middle  of  the 
stratigraphic  record. 

When  the  testimony  of  life  was  similarly  rescrutinized, 
with  as  much  freedom  from  inherited  presumptions  as 
possible,  it  failed  to  show  clear  evidence  that  the  early 
atmosphere  was  in  any  essential  respect  different  from 
the  atmosphere  of  the  later  ages,  particularly  when  the 
units  of  comparison  embraced  an  adequate  lapse  of 
time  to  cover  the  cycles  of  variation.  Even  when  the 
inquiry  was  pushed  back  to  the  very  earliest  strata 
that  carried  a  good  record  of  the  life  of  the  times,  not 
only  was  the  inherited  view  found  wanting  in  clear 
support,  but  adverse  evidence  accumulated  rather  than 
disappeared. 

When  the  inquiry  was  pressed  still  farther  back,  and 
support  for  the  postulate  of  a  molten  globe  was  sought 
in  the  crust  itself,  it  was  not  forthcoming.  With  strange 
perversity  the  supposed  granite  foundations  proved 
to  be  granitic  intrusions.  Thus  in  a  literal  sense  the 
very  foundations  of  the  old  view  proved  illusive. 

It  was  thus  that  the  trail  was  followed  back,  with  a 
weakening  faith  in  the  inherited  theory,  till  the  borders 
of  the  primitive  stage  were  reached.  But  one  further 
step  remained— to  examine  the  cosmogonic  postulates 
themselves.  Could  the  earth  ever  have  had  the  vast 
hot  atmosphere  postulated  ?  Was  the  earth's  gravity 
sufficient  to  hold  so  vast  and  vaporous  an  envelope  at 


INTRODUCTION  9 

such  high  temperatures  and  in  such  an  intense  state 
of  molecular  activity  as  the  old  mode  of  genesis  assigned  ? 
Was  the  gaseo-molten  genesis  a  reality?  Thus  I  was 
already  across  the  pass  that  leads  from  the  land  of  rocks 
into  the  realm  of  cosmogonic  bogs  and  fens.  Its  mists 
were  already  gathering  over  the  path  ahead.  Strangely 
enough,  the  cold  trail  of  the  ice  invasion  had  led  by  this 
long  and  devious  path  into  the  nebulous  field  of  genesis. 


CHAPTER  I 

THE  GASEOUS  THEORY  OF  EARTH-GENESIS  IN  THE 
LIGHT  OF  THE  KINETIC  THEORY  OF  GASES 

THE   OLD   VIEW   OF   CASKS 

At  the  time  Laplace  put  forth  his  hypothesis  of  the 
origin  of  the  solar  system,  the  true  nature  of  gases  was 
unknown.  Just  what  view  of  their  nature  was  held  by 
him  we  are  not  warranted  in  stating  with  confidence;  not 
unlikely  it  was  the  view  that  was  current  during  the 
early  half  of  the  last  century,  which  regarded  the  mole- 
cule as  the  nucleus  of  concentric  spheres  of  alternating 
attraction  and  repulsion.  At  appreciable  distances,  the 
outer  spheres  of  attraction  prevailed,  and  the  molecules 
were  drawn  together.  When  the  molecules  were 
forced  somewhat  closer  together,  the  spheres  of  repulsion 
came  into  play  and  there  was  resistance  to  compression 
and  a  tendency  to  expansion.  When,  however,  the 
molecules  were  brought  into  extremely  close  relations 
by  cold  or  by  compression,  the  inner  spheres  of  attraction 
were  brought  into  play,  and  the  molecules  came  still 
closer  together  to  form  liquids  and  solids.  If  such  a 
view  was  entertained  by  Laplace,  it  was  not  unnatural 
for  him  to  suppose  that  gases  might  gather  about  a 
planet  to  any  extent,  or  gather  about  Ixxlies  much 
smaller  than  planets,  or  even  gather  together  without 
any  solid  nucleus  at  all.  And  so  the  gaseous  theory 
of  the  origin  of  the  earth  may  have  been  quite  con- 
sistent with  the  views  of  the  behavior  of  gases  current 

10 


THE  GASEOUS  THEORY  OF  EARTH-GENESIS      1 1 

when  it  was  given  to  the  world,  however  much  it  may 
be  found  open  to  criticism  from  a  new  point  of  view  aris- 
ing from  a  new  theory  of  gases. 

While  this  defense  is  due  the  author  of  the  nebular 
hypothesis  and  his  earlier  followers,  it  is  none  the  less 
fair  to  put  an  old  gaseous  theory  of  earth  genesis  to  the 
test  of  a  new  theory  of  gases.  The  Laplacian  hypothesis 
of  the  origin  of  the  earth  is  eminently  a  gaseous  theory. 
It  is  indeed  entitled  to  be  regarded  as  the  type  of  gaseous 
cosmogonic  theories.  It  has  the  merit  of  being  specific 
and  systematic  beyond  most  of  its  class.  It  is  brought 
definitely  home  to  the  special  case  of  the  earth.  No 
other  of  its  class  has  these  eminent  merits  in  equal 
degree.  It  will  therefore  be  treated  in  this  discussion 
as  the  representative  of  its  class,  and  scant  space  will 
be  given  to  those  cruder  theories  that  are  not  clear  and 
specific  in  their  application  to  the  origin  of  the  earth,  for 
the  earth  is  the  one  celestial  body  of  which  we  have  a 
sufficiently  intimate  knowledge  to  make  it  susceptible 
of  satisfactory  use  as  a  test  of  theories  of  planetary  origin. 

THE    KINETIC  VIEW   OF   GASES 

Since  the  great  French  astronomer  and  mathematician 
framed  his  hypothesis — a  little  more  than  a  century  ago 
—much  has  been  learned  of  the  molecule  and  of  its  mode 
of  action,  especially  its  mode  of  assembling  to  form 
gases.  Much  more  is  yet  to  be  learned  no  doubt,  but  a 
real  start  has  been  made.  With  marvelous  skill,  physi- 
cists have  begun  to  deal  with  single  electrons  and  alpha- 
particles  and  to  toy  with  single  ions  and  atoms  of 
electricity.  It  may  almost  be  said  that  a  personal 
diagnosis  of  a  molecule  is  now  in  order;  as  also  a  detailed 


12  THE  ORIGIN  OF  THE  EARTH 

story  of  its  mode  of  joining  its  neighbors  in  assemblages 
to  form  a  gas,  and  of  its  behavior  toward  its  neighbors; 
for  a  molecule  is  not  a  gas  but  merely  one  of  many  of  its 
kind  to  make  a  gas.  Gases  are  congregations;  an 
atmosphere  is  a  great  congregation  drawn  together  by  a 
commanding  attraction. 

Now  it  is  quite  certain  that  a  molecule  is  not  a  little, 
round,  hard,  uncuttable  thing  surrounded  by  concen- 
tric layers  of  attraction  and  repulsion,  as  once  Imagined, 
nor  is  it  even  a  group  of  little,  round  uiuuttubles  so 
surrounded.  It  cannot  be  piled  up  indefinitely  in  the 
easy  way  once  so  conveniently  taken  for  granted  unless 
there  is  an  adequate  commanding  force.  It  is  already 
known  that  the  molecule  is  a  very  active  little  btxly,  a 
fidgety  midget,  always  apparently  in  a  whirl  or  a  quiver. 
So  true  is  this  that  two  molecules  could  scarcely  be 
brought  together,  however  gently,  in  such  a  way  that 
they  would  rest  quietly  side  by  side.  The  whirl  or  the 
quiver  of  one  or  the  other,  or  of  both,  would  be  almost 
sure  to  send  them  apart  with  a  sharp  recoil  (unless  there 
is  a  special  attraction  which  brings  on  chemical  union; 
but  this  lies  outside  the  present  problem).  In  our  atmos- 
phere, the  gravity  of  the  earth  is  always  pulling  the 
molecules  together.  If,  in  the  course  of  their  collisions 
and  recoils,  a  start  toward  a  vacuum  is  made,  a  crowd 
of  molecules  from  all  sides  is  pulled  or  pushed  into  it  by 
gravity,  and  there  is  a  little  crush  and  a  new  set  of  recoils 
springs  from  this.  In  some  such  ways  as  this,  it  comes 
about  that  the  molecules  of  an  atmosphere  are  per]>etually 
living  to  and  fro,  colliding  and  rebounding,  and  these 
collisions  and  rebounds  follow  one  another  with  extraordi- 
nary frequency.  The  late  Clerk-Maxwell,  a  mathe- 


THE  GASEOUS  THEORY  OF  EARTH-GENESIS   13 

matician  and  physicist  of  singular  acuteness  of  insight, 
computed  that  the  number  of  collisions  and  rebounds 
that  commonly  take  place  in  the  air  about  us,  under 
ordinary  conditions,  is  several  billions  per  second. 
The  frequency  is  greater  for  the  molecules  of  low 
specific  weights  than  for  those  of  higher  specific 
weights,  and  the  speeds  of  the  lighter  molecules  are 
the  greater. 

The  collisions  and  recoils  also  increase  in  number  and 
vigor  with  rise  of  temperature.  It  is  to  our  purpose 
to  make  special  note  of  the  fact  that  the  velocities  of  the 
molecules  in  their  recoils  increase  both  with  the  tempera- 
ture and  with  the  lowness  of  their  specific  weights. 
Light  molecules  are  likely  to  be  swift  molecules. 

PLANETARY   CONTROL   OF   GASES 

Now  in  the  case  in  which  we  are  specially  interested, 
the  gaseous  envelope  of  a  planet,  the  assembling  power— 
and  the  holding  power  -is  the  gravity  of  the  planet. 
It  thus  becomes  a  vital  question  how  large  a  congrega- 
tion of  molecules  a  given  planet  can  draw  together 
and  how  well  it  can  hold  them.  The  chief  difficulty  in 
retaining  the  entire  assemblage,  for  any  length  of  time, 
lies  in  the  extreme  activity  of  the  molecules,  and  in  the 
swiftness  of  their  rebounds  as  they  spring  back  from 
collisions  with  one  another.  The  molecules  are  very 
elastic;  if  they  are  not  perfectly  clastic,  as  commonly 
assumed,  they  are  immeasurably  near  it.  So,  when  they 
collide,  there  is  a  new  set  of  velocities,  and  the  nature  of 
the  new  set  depends  in  part  on  the  way  in  which  they 
strike  one  another  and  the  way  in  which  they  rebound, 
in  part  on  the  temperature,  and  in  part  on  other  features 


14  THE  ORIGIN  OF  THE  EARTH 

of  the  particular  case,  including  the  rotations  and  vibr 
tions  that  happen  to  be  affecting  the  molecules.  S 
also,  there  arises  a  new  set  of  directions  of  motio: 
and  this  also  depends  on  the  way  the  collisions  take  pla< 
and  on  the  other  factors  of  the  case.  The  collisions  a 
so  many  and  the  results  so  various  that  they  cannot  I 
dealt  with  individually  but  only  by  grand  averages  an 
by  the  laws  of  probability.  It  is  greatly  to  our  purpos 
however,  to  know  that  some  molecules  gain  in  vclocit; 
while  others  lose;  that  each  new  collision  almost  certain! 
raises  or  lowers  the  individual  speeds  of  the  molecuL 
involved.  And  so  it  happens  that,  by  virtue  of  ti 
chances  that  arise  in  a  great  series  of  collisions,  some  or 
molecule  may  be  given  higher  and  higher  speeds  in  su< 
cession  up  to  any  calculable  amount;  while  some  othi 
molecule,  by  way  of  offset,  may  fall  lower  and  lower  i 
velocity  until  it  is  stopped  altogether.  In  such  a  cas 
of  course,  it  remains  still  only  until  it  is  hit  again  and  s< 
"off  in  a  new  scries  of  experiences.  The  directions  whic 
the  molecules  take  in  rebounding  are  various  to  a 
indefinite  degree  and  practically  cover  all  direction 
These  perpetual  changes  of  speed  and  of  direction  affec 
all  the  molecules  drawn  into  an  atmosphere  about 
planet. 

As  already  remarked,  these  velocities  cannot  b 
dealt  with  individually  because  of  their  immense  numbei 
and  the  rapidity  of  their  changes;  but  Clerk-Maxwel 
Boltzmann,  and  others  have  shown  that  the  partition  an 
distribution  of  energies  and  of  velocities  are  expresse 
by  the  law  of  probabilities,  a  law  which  holds  with  grea 
fidelity  when  prodigious  numbers  of  events  of  a  kind  ar 
involved;  and  this  is  eminently  the  fact  in  this  cas< 


THE  GASEOUS  THEORY  OF  EARTH-GENESIS-     15 

At  all  times,  according  to  this  law,  the  speeds  of  certain 
proportions  of  the  molecules  will  rise  above  the  mean 
velocity  to  given  higher  and  higher  velocities  up  to  a 
theoretically  infinite  speed  for  a  vanishing  number,  or,  on 
the  other  hand,  will  fall  lower  and  lower  down  to  zero 
speed. 

Now  this  is  quite  to  the  purpose  of  the  test  we  wish 
to  make,  for  we  may  learn  from  this  law  how  often  a 
given  molecule  will  acquire  a  speed  sufficient  to  enable 
it  to  get  away  from  the  control  of  the  planet,  if  other 
conditions  are  favorable.  Under  the  law  of  probabilities, 
any  molecule  of  a  planet's  atmosphere  may,  in  infinite 
time,  acquire  a  velocity  high  enough  to  escape  in  spite  of 
the  planet's  gravity,  if  other  conditions  do  not  prevent.1 
We  must  therefore  look  well  to  these  other  conditions, 
for  much  depends  upon  them. 

THE   ERRONEOUS  AND   THE   TRUE  CRITICAL  VELOCITY 

Now  let  us  look,  for  a  moment,  at  the  other  side  of  the 
equation,  the  holding  power  of  the  planet.  If  it  were 
possible  for  the  planet  to  be  alone  in  space,  its  gravity 
could  overcome  the  motion  of  a  molecule  moving  away 
from  it  in  all  cases  in  which  the  speed  of  the  molecule 
is  less  than  the  velocity  it  would  acquire  if  it  fell  from  an 
infinite  distance  to  the  planet,  free  from  interferences 
of  all  kinds.  If  the  molecule  has  this  "  velocity  from 
infinity,"  or  a  higher  velocity,  it  will  go  out  to  infinity,  in 
theory;  in  reality,  it  will  continue  to  go  away  indefi- 
nitely but  slower  and  slower  because  of  the  backward  pull 
of  the  planet's  gravity,  which,  however,  grows  feebler 
and  feebler  as  the  molecule  gets  farther  and  farther 
off;  the  attraction  of  the  planet,  however,  will  never 


1 6  THE  ORIGIN  OF  THE  EARTH 

overcome  the  molecule's  flight  entirely.  The  limit  of  a 
planet's  control  over  free  molecules  under  these  ideal 
conditions  is  then  this  "velocity  from  infinity." 

The  same  fact  may  be  put  in  another  way.  and  that 
gives  another  picture,  and  another  name.  If  a  molecule 
is  shot  out  from  the  earth  on  an  unobstructed  path  with 
a  velocity  such  that  the  path  becomes  an  ellipse,  the 
gravity  of  the  earth  will  bring  it  back;  but  if  it  is  shot 
out  with  a  velocity  such  that  its  path  becomes  a  parab- 
ola, it  will  not  return.  And  so  the  limit  of  the  planet's 
power  of  control  is  known  as  the  ''parabolic  velocity." 
The  "parabolic  velocity"  is  the  same  as  "the  velocity 
from  infinity,"  in  the  case  of  any  planet.  A  still  higher 
velocity  gives  a  hy]x?rbolic  path.  A  velocity  sufficient 
to  give  a  molecule  a  parabolic  path  or  a  hyperbolic  path 
is  beyond  the  planet's  control  even  when  the  planet  is 
quite  alone  in  space  and  there  are  no  other  planets,  or 
suns,  or  other  bodies,  to  help  it  escape  by  attraction 
counter  to  that  of  the  planet.* 

For  the  surface  of  the  earth  the  ''parabolic  velocity," 
or  ''velocity  from  infinity,"  is  about  11.2  kilometers, 
or  6.9  miles,  per  second.  It  follows  that  if  a  molecule 
acquires  a  velocity  of  this  magnitude,  and  is  directed 
away  from  the  earth,  and  has  a  free  path,  it  will  escape 

*.\  misleading  impression  has  gained  some  current  y  from  a  lack  of 
precision  of  statement  in  certain  treatises.  In  military  science,  it  is 
customary  to  compute  the  flight  of  projectiles  as  though  their  paths 
were  (xirabolas.  This  is  a  convenient  approximation,  but  is  not  rigor- 
ously accurate,  though  often  quoted  as  though  it  st<xxl  for  the  strict 
law  of  all  such  projectiles.  When  men  go  out  to  shoot  at  one  another, 
convenience  in  computation  may  l>c  indulged  and  some  latitude  in  lan- 
guage is  quite  sure  to  come  into  use,  but  it  is  not  projxjr  to  transfer 
either  the  indulgence,  the  language,  or  the  pur|>oses  they  serve,  to  the 
celestial  realm. 


THE  GASEOUS  THEORY  OF  EARTH-GENESIS      17 

from  the  earth's  control.  It  would  do  so  even  if  the 
earth  were  quite  alone  in  space  and  there  were  no  rival 
bodies  trying  to  pull  the  molecule  away.  This  velocity 
has  commonly  been  taken  as  the  "critical  velocity"  of 
escape — "critical"  because  it  was  thought  that  all 
velocities  below  this  could  be  controlled  by  the  earth, 
while  all  above  it  could  not  be.  But  this  notion  needs 
rectification.  For  the  imaginary  case  of  a  planet  com- 
pletely isolated  in  space,  it  holds  good.  But  no  planet 
is  isolated  in  space;  it  could  not  be  so  isolated  and  be  a 
planet.  There  must  be  a  sun  where  there  is  a  planet, 
and  in  our  system  there  is  a  family  of  planets  and  satel- 
lites. Now  if  a  molecule  is  shot  away  from  the  earth 
toward  Jupiter,  that  giant  planet  pulls  the  molecule 
toward  it,  while  the  earth  pulls  the  molecule  backward. 
The  degree  of  influence  felt  by  the  molecule  is  the 
difference  between  the  pull  of  the  earth,  near  at  hand, 
and  the  pull  of  Jupiter,  far  oil.  The  Jovian  effect,  how- 
ever, because  of  distance,  is  minute  and  negligible.  But 
when  the  great  attraction  of  the  sun  is  brought  into 
competition  with  that  of  the  earth,  as  it  necessarily  is  at 
all  times,  the  case  takes  on  a  new  aspect.  It  is  clear, 
even  to  the  layman,  that  a  molecule  can  go  no  great 
fraction  of  the  distance  to  the  sun  before  the  attraction 
of  that  great  body  on  it  will  be  superior  to  that  of  the 
earth.  As  a  matter  of  fact,  there  is  only  a  comparatively 
small  space  about  our  planet  within  which  its  gravity 
is  even  differentially  greater  than  that  of  the  sun,  for 
the  sun  rules  the  whole  space  of  the  solar  system  in  a 
lordly  way.  There  is  merely  reserved  a  small  spheroid 
about  each  of  the  planets  that  is  under  their  own  con- 
trol primarily;  even  over  this  the  sun  holds  indirect  sway 


1 8  THE  ORIGIN  OF  THE  EARTH 

by  reason  of  its  control  over  the  planets  themselves. 
The  space  about  the  earth  within  which  its  gravity  is 
sufficient  to  draw  a  body  to  it  against  the  direct  attrac- 
tion of  the  sun  is  its  "sphere  of  influence,"  or,  in  terms 
better  suited  to  our  purposes,  its  ''sphere  of  control." 
If  a  molecule  is  placed  outside  this  space,  with  only  the 
common  motion  of  the  solar  system,  it  will  be  directly 
controlled  by  the  sun;  if  within  this  space,  it  will  be 
directly  controlled  by  the  earth. 

This  "sphere  of  control"  is  not  a  true  sphere,  but 
rather  a  spheroid  of  three  unequal  axes.  The  minimum 
radius,  according  to  Dr.  F.  R.  Moulton.  is  about 
1,000,000  kilometers,  or  620,000  miles;  the  maximum 
radius,  about  1,500,000  kilometers,  or  0^0,000  miles. 
The  dimensions  vary  as  the  earth  approaches  or  recedes 
from  the  sun,  but  this  is  immaterial  to  our  purpose 
except  as  showing  that  the  earth's  sphere  of  control 
is  not  a  fixed  feature;  it  is  rather  a  creature  of 
circumstances. 

Now,  the  true  "critical  velocity"  of  escape  is  the 
velocity  acquired  by  a  fall,  not  from  an  infinite  distance, 
but  from  this  limit  of  the  sphere  of  control,  about  1,000,- 
ooo  kilometers,  or  at  most,  1,500.000  kilometers  from 
the  center  of  the  earth.  The  difference  between  a  fall 
from  infinity  and  a  fall  from  1,000,000  kilometers  seems 
something  enormous,  but  the  difference  in  the  velocities 
acquired  is  by  no  means  so  serious  as  it  might  seem,  for 
by  far  the  larger  part  of  the  velocity  of  a  Ixxly  falling 
toward  the  earth  is  gained  in  the  lower  portion  of  the 
fall.  In  numerical  value  the  rectification  required 
is  more  nearly  like  that  of  replacing  a  meter  measure  by 
a  yardstick.  Hut  the  rectification,  though  not  large 


THE  GASEOUS  THEORY  OF  EARTH-GENESIS      19 

numerically,  is  radical  in  importance,  as  we  shall  see 
later,  for  it  affects  the  mode  of  escape  of  molecules  as 
well  as  the  velocity  of  escape. 

THE   ULTRA- ATMOSPHERES 

We  must  now  go  aloft,  for  the  whole  issue  lies  there, 
the  modes  of  escape  and  all.  It  is  of  little  moment  how 
great  a  velocity  a  molecule  may  acquire  in  the  lower 
air,  or  how  often  it  acquires  it;  it  cannot  escape,  for  it  is 
closely  surrounded  on  all  sides  by  an  atmosphere  that 
acts  as  a  barrier.  It  can  only  plunge  into  the  multitude 
of  molecules  that  crowd  about  it,  and  in  so  doing  dissi- 
pate its  energy  and  damp  its  velocity.  It  is  only  in  the 
extremely  thin  air  of  the  higher  regions  that  a  molecule 
can  find  a  clear  path  by  which  to  escape.  Let  us  then 
go  aloft  and  see,  as  well  as  we  may,  the  state  of  things 
there;  let  us  go  up  by  steps,  not  only  to  the  heights 
usually  set  as  the  limits  of  the  atmosphere,  but  all  the 
way  up  to  the  limit  of  the  sphere  of  control. 

In  the  lower  levels,  the  paths  of  the  molecules  between 
collisions  are  extremely  short  and  hence  straight,  for  the 
gravity  of  the  earth  can  bend  their  paths  in  only  an 
infinitesimal  way  in  the  small  fraction  of  a  second 
occupied  in  their  flights.  But  higher  up,  where  the 
molecules  are  sparser,  the  paths  between  collisions 
become  longer  and  slight  curvatures  begin  to  appear. 

Still  farther  up,  where  the  molecules  are  widely 
scattered,  the  curvatures  grow  more  pronounced.  When 
the  scattered  condition  becomes  still  greater,  the  earth's 
gravity  may  stop  the  outward  flight  of  some  molecules 
that  have  rebounded  outward  before  a  collision  takes 
place,  and  this  gravity  may  cause  them  to  turn  back 


THE  ORIGIN  OF  THE  EARTH 

on  elliptical  curves  toward  the  earth.  When,  with] 
still  further  ascent,  the  air  grows  attenuated  enough,! 
these  outward  flights  and  returns  without  collision 
come  to  be  the  dominant  feature. 

THE  KRENAL  ATMOSPHERE 

Thus  far  in  the  ascent,  we  have  followed  mainly  in 
the  footsteps  of  Dr.  Johnstonc  Stoney,'  the  pioneer  in 
this  field,  save  that  he  did  not  recognize  the  sphere  of 
control  and  the  qualifications  which  it  imjxises.  By 
an  analysis  of  the  case  he  saw  that  this  "fountain-like" 
action  must  become  the  prevalent  one  when  a  suflicicnt 
degree  of  atmospheric  rarity  is  reached,  and  directed 
attention  to  the  fountain-like  character  which  must 
thus  be  assumed  by  the  outer  atmosphere.  As  we  may 
find  the  term  "fountain-like"  cumbersome  for  the 
frequent  use  we  shall  want  to  make  of  it.  i>crhaps  we  may 
use  krcnal  in  its  stead,  for  this  means  the  same.  It  ; 
will  serve  our  convenience  to  distinguish  this  upper 
region  as  the  krctml  /one.  and  the  lower  region  as  the 
collisional  zone,  since  the  latter  is  colli.sjonal  in  a  singu- 
larly intense  degree. 

In  the  picture  of  the  atmosphere  delineated  by 
Stoney,  the  zone  of  fountain-like  or  krcnal  loops  served 
as  the  outer  atmospheric  border.  The  picture  is  not 
without  its  beauty,  the  whole  summit  of  the  atmosphere 
a  mass  of  vaulting  molecules,  describing  loops  of  multi- 
tudinous forms  and  dimensions  set  in  all  jxwsible  direc- 
tions. 

Under  the  law  of  probabilities  applied  to  molecular 
velocities,  some  of  these  vaults  must  reach  the  limit 
of  the  sphere  of  control,  some  must  go  beyond,  but 


THE  GASEOUS  THEORY  OF  EARTH-GENESIS      21 

the  greater  multitude  must  fall  short  in  various  degrees. 
Those  molecules  that  leap  beyond  the  limit  of  the 
earth's  control  enter  the  sun's  sphere  of  control,  where, 
they  pass  into  orbits  about  the  sun  and  are  lost  to  the 
earth's  atmosphere.  This  is  the  first  and  simplest  mode 
of  escape,  the  single  leap,  the  only  mode  commonly 
recognized  in  the  past,  but  in  reality  not  the  only  mode. 

The  krenal  zone  of  the  atmosphere  is  thus  pictured  as 
reaching  from  the  collisional  atmosphere  outward  to 
the  limit  of  the  sphere  of  control.  The  molecules  in 
this  zone  are  highly  dispersed  in  its  lower  parts  and 
they  grow  more  and  more  scattered  toward  the  outer 
limit.  It  is  wise  to  emphasize  the  extremely  scattered 
state  of  the  krenal  molecules,  especially  in  the  outer- 
most zone,  but  it  is  an  error  to  ignore  their  existence  or 
importance.  Because  the  krenal  atmosphere  is  so 
much  more  attenuated  than  the  lower  atmosphere,  it 
will  be  conservative  to  call  it  an  ultra-atmosphere. 

THE   ORBITAL  ATMOSPHERE 

But  we  may,  however,  not  complete  our  picture  of 
the  atmosphere,  as  Dr.  Stoney  seems  to  have  done,  with 
a  beautiful  mantle  of  krenal  loops  enveloping  the  colli- 
sional atmosphere.  The  vaulting  molecules  are  liable 
to  collision  at  any  point  in  the  course  of  these  krenal 
loops,  and,  under  the  law  of  probabilities,  such  collisions 
are  quite  sure  to  occur.  The  rebounding  molecules 
may  strike  in  any  direction,  as  in  other  cases  of  collision, 
and  there  may  be  all  the  varieties  of  partitions  of 
energy  and  of  redistributions  of  motion  that  take 
place  between  colliding  molecules  in  other  cases.  It 
follows  that  a  certain  percentage  of  the  rebounding 


22  THE  ORIGIN  OF  THE  EARTH 

molecules  will  move  more  or  less  parallel  to  the  earth's 
surface,  and  a  certain  proportion  of  them  will,  under  the 
laws  of  partition  of  motion,  have  velocities  high  enough 
to  carry  them  into  orbits  about  the  earth.  In  pro- 
portion as  the  new  courses  approach  parallelism  to  the 
earth's  surface,  the  molecules  will  escaj>e  the  denser 
atmosphere,  and  will  continue  to  circle  about  the  earth 
indefinitely,  except  that  sooner  or  later  they  are  likely 
to  meet  some  molecule  of  their  own  class  in  an  orbit  that 
happens  to  cross  their  own,  or  some  vaulting  molecule 
in  the  course  of  its  krenal  flight.  Hut  for  these  con- 
tingencies, they  would  have  reached  a  condition  of 
stable  motion,  since  orbits  are  admirable  types  of 
stability  and  jxr]>etuity.  It  is  a  really  curious  transi- 
tion for  a  molecule  to  pass  by  a  series  of  gradations  from 
such  an  extremely  jostled  state  as  prevails  in  the  lower 
atmosphere,  where  it  was  suffering  several  billion 
diversions  or  reversals  of  motion  per  second,  into  a  steady 
orbital  motion  in  which  it  follows  an  orderly  curving 
path  for  an  indefinite  period.  These  orbital  molecules 
thus  form  a  quite  marked  class,  and  constitute  a  third 
element  of  the  earth's  atmosphere,  an  additional  ultra- 
atmosphere  -the  orbital  atmosphere. 

To  unify  the  new  picture,  let  us  reflect  that  on  logical 
analysis  it  appears  clear  that  atmospheric  molecules  are 
actuated  by  three  quite  distinct  mcxles  of  action,  though 
derivable  the  one  from  the  other  the  collisional,  the 
krenal,  and  the  orbital.  Designating  the  molecules  of 
each  class  as  an  atmosphere,  they  constitute  ( i )  the  com- 
mon or  collisional  atmosphere,  (2)  the  krenal  atmosphere 
or  ultra-atmosphere,  and  (3)  the  orbital  atmosphere  or 
ultra-atmosphere. 


THE  GASEOUS  THEORY  OF  EARTH-GENESIS   23 


paths  of  the  orbital  molecules  lie  solely  in  the 
outer  portion  of  the  sphere  of  control.  They  cannot  be 
perpetuated  or  even  developed  in  the  collisional  zone 
because  of  the  interference  of  other  molecules,  nor  can 
orbital  paths  be  maintained  for  any  appreciable  length 
of  time  in  the  denser  part  of  the  krenal  zone,  for  lack 
of  sufficiently  long  free  paths.  They  can  persist  only 
in  the  extremely  attenuated  portion  of  the  krenal  zone 
where  the  contingencies  of  collision  are  relatively  small. 
Molecules  in  orbital  flights  and  in  krenal  flights  thus 
cross  and  recross,  in  their  very  open  fashion,  a  common 
area,  the  outer  part  of  the  sphere  of  control,  which 
neither,  nor  both,  can  be  said  to  fill,  but  only  sparsely 
to  traverse.  In  this  common  area  these  two  kinds  of 
flights  cross  one  another,  the  krenal  directed  chiefly 
outward  and  inward,  the  orbital  more  or  less  laterally 
and  curvingly.  The  law  of  probabilities  implies  that 
a  certain  number  of  collisions  will  take  place  between 
the  vaulting  molecules  and  the  orbital  molecules.  So, 
too,  since  the  orbital  molecules  circle  round  the  earth  in 
various  directions  in  orbits  of  various  dimensions  and 
configurations,  though  all  elliptical,  it  follows  that  a 
certain  proportion  of  these  will  also  collide  with  one 
another. 

THE   PROGRESSIONAL  MODE   OF   ESCAPE 

Now  when  such  collisions  take  place,  the  molecules  in 
orbits  may  either  be  driven  earthward  into  smaller 
orbits  —  which  may  not  unlikely  strike  into  the  collisional 
atmosphere  —  or  else  be  driven  outward  into  larger  orbits. 
One  or  another  of  these  results  is  almost  certain  to  follow 
any  collision  that  may  happen  to  molecules  in  the  course 


24  THE  ORIGIN  OF  THE  EARTH 

of  their  orbital  flights,  whether  they  encounter  one  of 
their  own  class  or  a  molecule  in  krenal  flight.  Thus  it 
appears  that  krenal  molecules,  as  an  incident  of  their 
vaulting  flights,  may  not  only  drive  molecules  into 
orbital  flights,  but  may  change  these  flights  into  larger 
or  smaller  orbits,  and,  under  the  law  of  probabilities, 
will  inevitably  do  both  these  things  in  a  certain  per- 
centage of  cases.  Now,  it  is  obvious  that  in  the  course 
of  such  changes  of  orbit,  the  limit  of  the  sphere  of  control 
will  be  passed  in  a  certain  j>ercentage  of  cases,  and  the 
molecule  will  escajK*  from  the  ultra-atmosphere. 

Here  then  is  a  second  mode  of  molecular  escape, — escape 
by  a  series  of  orbital  changes.  In  the  single  mode  of 
escape  heretofore  commonly  recognized,  the  molecules 
must  vault  by  single  leaps  from  jx>ints  in  the  collisional 
atmosphere  into  space  Ixryond  the  limit  of  control.  They 
must  then  have  at  least  the  4t  critical  velocity."  In  the 
mode  of  escaj>e  just  set  forth,  the  molecules  pass  from 
the  collisional  atmosphere  outward  step  by  step.  The 
accession  of  velocity  at  any  one  time  need  be  little  more 
than  what  Ls  requisite  to  give  the  molecules  revolutionary 
courses  about  the  earth. 

For  a  circular  orbit  the  velocity  of  revolution  is  to  the 
parabolic  velocity  as  1:1  2,  or  1:1.4+.  The  velocity 
necessary  for  escape  is  notably  less  than  the  parabolic 
velocity  as  already  jx>inted  out. 

The  recognition  of  this  second  mode  of  cscajx,*  makes 
necessary  a  second  rather  large  correction  in  conclu- 
sions adverse  to  atmospheric  escaj>e  that,  in  spite  of  the 
fact  that  they  were  based  on  the  erroneous  assumption 
that  the  parabolic  velocity  is  the  critical  velocity  and 
that  escape  takes  place  only  by  single  leaps  from  the 


THE  GASEOUS  THEORY  OF  EARTH-GENESIS      25 

imagined  surface  of  the  collisional  atmosphere,  have  had 
currency.  Escape  by  the  progressive  orbital  method 
does  not  require  more  than  about  five-sevenths  of  the 
velocity  requisite  for  escape  by  a  single  leap,  and  that 
may  be  acquired  by  instalments  without  necessary 
loss  of  preceding  increments.  There  may  be  many 
steps  in  every  escape;  and  indeed  there  may  be  many 
backward  steps  mingled  with  the  forward  steps.  So,  too, 
the  time  that  elapses  between  the  successive  steps  may 
be  long  or  short  to  indefinite  degrees,  for  the  interval 
depends  merely  on  the  contingency  of  the  next  col- 
lision which  is  indeterminate.  A  molecule  pursuing  an 
orbit  continues  its  revolutions  indefinitely  until  a  collision 
arises  to  make  it  do  otherwise.  It  follows  that  the  total 
time  taken  in  effecting  an  escape  is  indeterminate,  and 
may  be  long.  This  gives  a  distinctly  new  aspect  to  the 
whole  problem  of  molecular  escape  from  the  atmosphere. 

ATMOSPHERIC   INTERCHANGES   AND   EQUILIBRIA 

But  we  are  not  quite  at  the  end  of  the  logical  chain 
yet.  When  molecules  pursuing  orbital  courses  about 
the  earth  are  forced  across  the  limit  of  control  into 
orbital  courses  about  the  sun,  they  must  return  to  the 
points  of  their  last  collisions,  in  the  natural  course  of 
things,  if  they  do  not  suffer  interferences  or  diversions 
of  one  kind  or  another  in  the  meantime.  These  points  of 
last  collision  were  within  the  sphere  of  the  earth's  control. 
So  these  molecules,  in  their  new  solar  orbits,  will  come 
back  into  or  cut  across  the  earth's  sphere  of  control. 
There  are  thus  definite  possibilities  that  some  of  these 
returning  molecules  of  the  earth's  atmosphere  will 
encounter  molecules  of  the  earth's  atmosphere  and  that 


26  TIIK  ORKilN  OF  TIIK  KAKTII 

the  collision  will  l>e  such  an  to  force  them  again  into 
orbits  under  the  control  of  the  earth  or  into  courses 
that  will  plunge  them  into  the  denser  atmosphere  about 
the  earth.  Here  is  a  definite  method  of  recover)'  of 
esca|>ed  molecules  after  they  have  In-come  member*  of 
the  sun's  ultra-atmosphere. 

In  like  manner,  molecules  that  revolve  about  the  sun 
as  members  of  its  ultra  atmosphere,  even  though  they 
were  never  previously  members  of  the  earth's  atmos- 
phere, may  cut  through  the  earth's  sphere  of  control 
and  thus  IK*  liable  to  a  collision  with  an  atmospheric 
molecule  and  as  a  result  be  incoq>oratcd  in  the  earth 'ft 
atmosphere.  The  same  logic  and  the  same  laws  that  we 
have  found  applicable  to  the  atmosphere  of  the  earth 
are  applicable  also  to  the  atmosphere  of  the  sun.  It 
must  have  its  krenal  ultra-atmosphere  and  its  orbital 
ultra-atmosphere.  These  ultra  atmospheres  of  the  sun 
are  required  by  the  logic  of  the  case  to  reat  h  out  not  only 
to  the  earth,  but  to  the  limits  of  the  sun's  sphere  of 
control.  This  lies  very  far  outside  tin-  outermost  planet. 
There  is  thus  not  only  a  threefold  phase  of  the  solar 
atmosphere,  as  well  as  of  the  planetary  atmospheres,  but 
the  krentil  timl  the  orhil<il  phases  of  tin  W«/r  atmosphere 
envelop  the  atmospheres  of  till  the  pltinets. 

It  thus  appears  that  passages  of  molecule*  from  the 
sphere  of  control  of  the  sun  into  the  sphere  of  control  of 
the  earth,  and  the  reverse,  are  inevitable  consequences 
of  the  kinetic  theory  of  gases,  unless  there  l>e  agencies 
that  contravene  to  prevent  the  logical  consequences  of 
kinetic  laws. 

It  is  imjMtrtant  to  observe  further  that  such  inter- 
changes of  molecules  tend  to  establish  an  equilibrium 


THE  GASEOUS  THEORY  OF  EARTH-GENESIS      27 

between  the  ultra-atmospheres  of  the  earth  and  the 
ultra-atmospheres  of  the  sun;  for  if  one  of  these  atmos- 
pheres becomes  more  plethoric  than  is  concordant  with 
its  relations  to  the  other,  it  will  inevitably  feed  more 
molecules  into  the  leaner  atmosphere  than  the  latter  will 
return  to  it.  In  this,  then,  there  is  a  reciprocal  process 
that  tends  to  equate  the  loss  and  gain  between  the 
planetary  ultra-atmospheres  and  the  solar  ultra- 
atmospheres.  This  reciprocity  tends  toward  the  main- 
tenance of  a  stable  condition  in  both. 

SUPPLKMKNTARY   AGKNCIES 

We  have  now  followed  far  enough  for  our  purposes  the 
intricate  system  of  actions  and  reactions  that  take  place 
in  the  atmospheres  of  the  solar  system.  We  have 
considered  them,  however,  wholly  apart  from  inci- 
dental or  co-operative  agencies,  though  we  have  referred 
to  the  possibility  of  contravening  agencies. 

There  are  probably  no  strictly  contravening  agencies, 
but  among  the  other  agencies  that  act  on  the  atmosphere 
there  are  some  that  interfere  with  or  modify  the  syste- 
matic development  of  the  ultra-atmospheres  we  have 
just  considered.  One  of  these,  to  which  passing  atten- 
tion must  be  given,  is  the  pressure  of  light.  As  in  the 
case  of  most  newly  discovered  agencies,  there  is  a  current 
tendency  to  call  on  light-pressure  for  services  it  is  in- 
competent to  perform.  It  is,  however,  probably  a 
factor  in  the  feeding  and  depletion  of  planetary  atmos- 
pheres. It  is  probably  not  a  very  competent  factor, 
since  the  diameters  of  molecules  are  too  small  to  permit 
the  wave-action  of  light  to  act  ujx>n  them  efficiently 
except  |>crhaps  in  case  of  selective  absorption.  In  so 


28  THE  ORIGIN  OF  THE  EARTH 

far  as  light  is  absorbed  by  the  molecules,  the  propulsive 
energy  of  the  light  is  felt,  and  to  that  extent  the  mole- 
cules are  driven  in  the  direction  of  light -propagation. 

The  diminution  of  light  with  distance  follows  the 
same  law  as  the  distribution  of  gravitation.  There  are 
various  ways  in  which  light  is  lost  as  it  progresses, 
while  gravity  is  not  known  to  suffer  loss.  It  follows 
that  the  jxnvcr  of  light -pressure  compared  with  gravity 
is  greatest  near  the  luminous  Ixxly  from  which  it  origi- 
nates. Its  disjHTsive  jxiwcr  must  IK-  greatest  there, 
and  so  the  very  fact  that  the  sun  and  the  star*  hold  their 
gases  and  apparently  have  held  them  for  cons  in  spite 
of  the  light -pressure  seems  to  imply  that  the  latter 
can  be  at  best  only  a  limited  agency  of  disjxTsion. 
There  seems  no  ground,  therefore,  to  treat  it  as  more 
than  a  co-operating  agency  in  atmospheric  feeding  and 
dispersion. 

So  far  as  it  is  potent  at  all.  its  first  function  should 
IK*  the  disjx-rsion  of  the  outer  atmo>phcrc  of  the  sun. 
It  should  aid  in  counteracting  the  gravity  of  the  sun  and 
hence  in  facilitating  the  development  of  vaulting  and 
orbital  paths,  and  the  enlargement  of  the  orbital  paths 
as  a  part  of  its  systematic  work  in  causing  molecules  to 
move  out  from  the  sun.  In  the  cour>c  of  thoc  outward 
movements  the  earth  should  lx*  encountered  and  some 
of 'the  solar  molecules  should  Ix*  captured  by  it.  Such 
action  would  constitute  a  systematic  feeding  of  the 
earth's  atmosphere  at  the  expense  of  the  >un's  atmos- 
phere. 

On  the  other  hand,  the  light  of  the  sun  traversing  the 
sphere  of  the  earth's  control  transversely  should  tend 
to  drive  awav  some  of  the  molecules  of  the  ultra- 


THE  GASEOUS  THEORY  OF  EARTH-GENESIS      29 

atmospheres  of  the  earth,  and  thus  have  a  depleting 
effect  on  the  earth's  atmosphere.  We  may  assume 
for  present  purposes  that  the  feeding  and  depleting 
effects  offset  one  another  more  or  less  completely,  though, 
theoretically,  the  probabilities  of  gain  seem  to  lie 
somewhat  with  the  earth,  a  dark  body,  as  against  the 
sun,  a  brilliantly  luminous  body. 

It  is  highly  probable  that  electric  action  plays  an 
important  part  in  the  distribution  of  molecules  in  the 
rare  outer  zones  of  the  atmospheres  of  the  sun  and  its 
planets.  Rather  definite  hints  of  such  effects  may  be 
gathered  from  auroral  phenomena,  electric  storms,  the 
behavior  of  the  trains  of  meteorites  between  forty-live 
and  sixty  miles  above  the  surface,  the  ionizing  effects 
of  ultra-violet  light,  and  other  phenomena,  but  data 
for  confident  treatment  arc  as  yet  wanting. 

There  is,  however,  a  single  suggestion  of  such  vital 
relations  to  the  organic  function  subserved  by  the 
atmosphere  that  a  very  tentative  statement  of  its  nature 
may  be  justified  in  this  connection. 

There  is  reason  to  believe  that  the  violent  explosions 
of  the  sun  that  give  rise  to  ''eruptive  prominences" 
often  force  molecules  far  out  into  interplanetary  space 
and  that  the  electric  fields  of  the  sun,  of  the  prominences 
in  particular,  and  of  the  earth  have  a  selective  effect  on 
charged  molecules.  According  to  the  recent  brilliant 
determinations  of  Hale  and  his  colleagues,  the  surface 
charge  of  the  sun  is  dominantly  negative,  while  in  con- 
nection with  the  sun-spots,  to  which  the  prominences 
are  related,  there  are  great  vortices  of  gases  bearing 
high  negative  charges.  On  the  other  hand,  according 
to  recent  determinations,  the  atmosphere  of  the  earth  is 


30  THE  ORIGIN  OF  THE  EARTH 

dominant!)*  positive,  while  the  earth-body  is  dominantly 
negative.  These  suggest  that  electric  clillerentiations 
obtain  in  the  solar  system  with  |>crhaps  alternate 
arrangements  of  the  electric  charges.  However  this(may 
be,  these  charged  tracts  of  the  sun  and  of  the  earth  form 
a  suggestive  working  combination.  The  sun's  negative 
charge  must  tend  to  draw  to  it>clf  molecules  carrying 
positive  charges  and  tend  to  rejx-1  molecules  carrying 
negative  charges.  The  jx>sitivc  charge  of  the  earth's 
atmosphere,  on  the  contrary,  tends  to  draw  to  it  mole- 
cules of  negative  charge  and  re|H-l  those  of  |>ositive 
charge.  It  is  well  known  that  under  the  ordinary 
conditions  of  electrolysis  a  comjxisite  molecule  in  suffer- 
ing dissociation  yields  a  positive  charge  to  one  class  of 
elements  and  negative  charge  to  another  cla>s  and  that 
the  atmospheric  constituents  In-long  with  the  latter 
rather  than  the  former,  oxygen  in  particular  taking  the 
negative  charge.  The  experimental  evidence,  unfor- 
tunately, is  very  limited  in  cases  where  the  dissociation 
takes  place  in  other  than  aqueous  solutions,  particularly 
in  cases  analogous  to  that  in  hand.  However.  J.  J. 
Thomson  found  in  certain  experiments  that  oxygen  t<xjk 
up  free  electrons  while  in  the  course-  of  projection.  There 
is  also  some  additional  >up]xirl  for  the  assumption  that, 
by  means  of  the  electric  dissociation  which  doubtless 
attends  the  solar  eruptions,  oxygen  and  {R-rhaps  other 
atmospheric  constituents  receive  negative  charges. 
If  so,  they  sutler  electric,  as  well  as  mechanical,  pro- 
pulsion from  the  sun.  Such  elements  as  may  receive 
|x)sitive  charges  are  drawn  back  to  the  sun.  The  con- 
stitution of  the  atmosphere  of  the  sun  and  stars  seems 
to  Ix*  fairly  in  harmony  with  the  suggestion  of  a  jx>sitive 


THE  GASEOUS  THEORY  OF  EARTH-GENESIS      31 

electric  segregation,  while  the  nature  of  the  atmosphere 
of  the  earth  suggests  a  negative  segregation. 

There  are  several  other  sources  from  which  high 
molecular  velocities  might  arise  in  the  outer  atmosphere, 
as,  for  example,  the  plunge  of  meteorites  and  the  carrying 
aloft  of  minute  radioactive  particles,  but  their  quanti- 
tative value  is  too  questionable  to  require  consideration 
here. 

The  value  of  some  of  these  undetermined  factors  in 
promoting  the  escai>e  or  the  accession  of  molecules  is 
only  conjectural  at  present,  but  it  seems  unsafe  to  ignore 
them.  Xo  computation  relative  to  the  rate  of  escape 
of  the  earth's  atmosphere,  however  accurate  in  its 
mathematical  processes,  has  any  claim  to  serious  weight 
if  it  does  not  recognize  all  the  factors.  It  seems  espe- 
cially untrustworthy  if  it  does  not  give  full  consideration 
to  the  ultra-atmospheres  of  the  earth  and  of  the  sun, 
and  to  their  interplay.  To  include  all  these  certainly 
renders  the  case  intricate  in  the  extreme.  The  uncer- 
tainty as  to  the  values  of  the  several  co-oj>erative 
factors  lends  especial  embarrassment  to  all  efforts 
in  computative  lines.  The  geo-natunilist  endeavors 
to  circumvent  the  intricacies  of  these  complications 
by  search  for  vestiges  in  which  nature  herself,  having 
actually  made  the  correlation,  records  her  composite 
equated  result. 

Resecting  the  power  to  acquire  and  retain  atmos- 
pheres, the  bodies  that  attend  the  sun  give  a  fairly 
clear  answer,  as  Stoney  has  urged;  the  great  planets 
have  great  atmospheres,  the  terrestrial  planets  have 
small  atmospheres,  the  planetoids  and  satellites  little 
or  none  at  all.  Jupiter  has  undoubtedly  many  times 


32  THE  ORIGIN  OF  THE  EARTH 

more  atmosphere  than  all  the  terrestrial  planets,  planet- 
oids and  satellites  combined.  Among  the  terrestrial 
planets  the  atmospheres  seem  to  be  graded  strictly  in  the 
order  of  masses,  and  somewhat  nearly  in  proportion  to 
mass  when  modified  for  distance  and  temperature. 
The  law  of  Stoney  that  atmospheres  are  apportioned 
to  masses  has  strong  naturalistic  support.  Measurably 
so  has  the  philosophy  of  interchange  to  which  we  assign 
the  maintenance  of  such  atmospheres.  So  far  as  the 
special  features  of  maintenance  are  concerned,  the  natu- 
ralistic record  of  composite  results  appears  in  a  long  line 
of  phenomena,  partially  astronomical,  partly  biological, 
more  largely  geological,  to  which  some  allusion  has 
been  made  in  the  Introduction.  The  analysis  and 
interpretation  of  these  is  scarcely  less  embarrassed  by 
intricacies  and  unknown  factors  than  the  computative 
method.  Many  aspects  of  the  problem  of  atmospheric 
maintenance  must,  for  the  time  being,  remain  open. 
The  deployment  of  the  problem,  however,  may  serve 
to  restrain  unwarranted  claims  to  conclusive  determina- 
tions. 

THE  ATMOSPHERIC  TEST  OF  THE  LAPLACIAN  HYPOTHESIS 

The  revisions  and  extensions  of  the  kinetic  view 
of  our  atmosphere  involved  in  the  foregoing  sketch, 
particularly  the  orbital  atmosphere,  the  progressive  mode 
of  escape  of  molecules,  the  interchange  between  the  solar 
and  the  terrestrial  atmospheres  and  the  equilibrium 
between  these,  followed  rather  than  preceded  the 
atmospheric  test  of  the  Laplacian  hypothesis  to  which  we 
are  now  prepared  to  turn.  The  test  started  with  the 
older  kinetic  views  of  the  atmosphere,  particularly  that 


THE  GASEOUS  THEORY  OF  EARTH-GENESIS      33 

phase  of  them  advanced  by  Dr.  G.  Johnstone  Stoney.3 
The  very  suggestion  of  the  test  sprang  from  Stoney 's 
doctrine  that  a  planet  could  not  hold  an  indefinite 
amount  of  atmosphere  but  only  an  amount  proportionate 
to  its  mass  when  other  conditions  are  duly  considered. 
The  considerations  we  have  added  seem  to  supplement 
and  strengthen  this  point  of  view,  and  they  are  here 
given  in  anticipation  of  the  atmospheric  test  of  the 
validity  of  the  gaseo-molten  theory  of  the  origin  of  the 
earth. 

To  make  the  test  critically  it  was  thought  necessary 
to  take  into  account  the  fact  that  the  parabolic  velocity 
of  the  earth — which,  following  current  practice,  I  then 
took  as  the  critical  velocity  of  molecular  escape — 
decreases  with  the  altitude,  and  that  it  varies  with  the 
rate  of  the  earth's  rotation.4  To  assist  in  weighing  these 
factors,  Dr.  F.  R.  Moulton  was  kind  enough  to  prepare 
for  me  tables  of  the  variations  of  the  parabolic  velocity 
for  various  altitudes  with  adaptations  to  a  stationary 
earth,  to  an  earth  with  the  present  rotation,  and  to  an 
earth  rotating  in  one  .hour  and  twenty-four  minutes,  this 
last  being  the  rate  at  which  the  rotation  would  cause 
separation  by  centrifugal  action  at  the  equatorial 
surface.  Such  a  rotation  would  throw  the  atmosphere 
off  and  initiate  disruption  of  the  earth,  so  that  there  was 
no  need  to  consider  any  higher  rate  of  rotation.  Dr. 
Moulton  added  formulas  by  which  the  tables  could  be 
extended  or  modified  to  suit  such  other  cases  as  might 
be  selected.5  Dr.  A.  W.  Whitney  prepared  for  me  a 
table  of  the  velocities  that  would  be  acquired  by  the 
several  constituents  of  the  atmosphere  for  a  series  of 
temperatures,  and  also  a  table  of  the  frequency  at  which 


34  THE  ORIGIN  OF  THE  EARTH 

a  certain  percentage  of  molecules  would  acquire  speci- 
fied velocities.6  With  these  aids  a  series  of  representative 
cases  was  tested. 

One  of  the  gravest  difficulties  encountered  in  trying  to 
make  a  test  that  might  be  taken  as  conclusive  lay  in  the 
uncertainty  as  to  the  precise  state  of  things  in  the  upper 
atmospheric  levels,  an  uncertainty  which  was  then  par- 
ticularly great.  However,  it  is  sometimes  possible  to 
deal  with  a  question  in  a  really  conclusive  way  even  when 
the  precise  conditions  are  indeterminable,  if  it  happens 
to  be  possible  to  bring  under  test  a  graduated  series  of 
representative  cases  whose  combined  range  is  wide 
enough  to  cover  all  supposable  cases.  If  the  tests  show 
that  none  of  these  is  tenable,  the  entire  range  of  cases 
is  effectively  excluded,  and  it  is  immaterial  what  the 
details  of  the  actual  case  may  be. 

In  the  case  in  hand,  the  tests  did  not  make  it  altogether 
certain  that  a  white-hot  earth  could  not  hold  the  larger 
part  of  the  great  atmosphere  assigned  it,  for  the  rela- 
tively brief  period  during  which  the  putative  white-hot 
stage  would  last,  for  time  is  a  vital  factor  in  the  loss  of 
an  atmosphere.  It  did  appear,  however,  quite  doubtful 
whether  so  much  water-vapor  as  was  postulated  could 
have  been  held,  even  through  the  white-hot  stage,  be- 
cause its  molecular  activity  would  have  been  exception- 
ally high,  as  the  molecule  of  water  gas  is  relatively  light. 
There  would  also^have  been  liability  to  dissociation, 
which  would  give  rise  to  still  higher  molecular  activity. 

TEST  CARRIED  BACK  TO  POSTULATED  GASEOUS  GLOBE 

As  the  tests  applied  to  the  white-hot  stage  thus  seemed 
to  fall  somewhat  short  of. complete  conclusiveness,  the 


THE  GASEOUS  THEORY  OF  EARTH-GENESIS      35 

method  was  applied  to  the  next  earlier  stage  of  the 
earth  postulated  by  the  Laplacian  hypothesis,  when 
the  earth  was  entirely  gaseous  and  when  the  molecular 
activities  and  the  temperatures  were  still  higher  and 
the  chemical  dissociations  probably  more  extensive. 
Not  only  were  the  temperatures  at  that  stage  high 
enough,  by  hypothesis,  to  keep  even  the  refractory 
substances  of  the  earth  in  a  vaporous  state,  but  the 
vast  gaseous  globe  in  its  gaseous  state  must  have  been 
much  larger  than  in  its  later  stages,  and  hence  the 
velocity  required  for  the  escape  of  molecules  from  its 
outer  border  was  proportionately  less.  There  seemed 
good  reasons  for  thinking  that  hydrogen  would  be 
liberate'd  by  dissociation  at  such  temperatures.  Now 
the  earth  is  scarcely  competent  to  hold  hydrogen 
permanently  at  present  temperatures  and  at  the  present 
atmospheric  surface  where  the  gravity  effect  is  greater 
than  it  could  have  been  at  the  surface  of  the  postulated 
gaseous  globe.  These  and  other  considerations  seemed 
to  make  it  extremely  doubtful  whether  water-vapor,  or 
its  dissociated  constituents,  could  have  been  held 
under  control  on  the  outer  border  of  the  extremely  hot 
gaseous  spheroid.  This  conclusion  is  strengthened  by 
the  probability  that  such  a  very  hot  gaseous  spheroid 
would  be  affected  by  explosive  eruptions,  somewhat 
as  the  sun  is.  Violent  ejections  of  such  a  type  would 
without  doubt  have  greatly  aided  the  discharge  of  the 
more  active  gases. 

TEST  APPLIED   TO   THE   POSTULATED  NEBULAR  RING 

But,  to  cover  the  last  remnant  of  doubt,  the  test  was 
carried  still  another  step  backward  and  applied  to  the 


36  THE  ORIGIN  OF  THE  EARTH 

postulated  stage  at  which  the  substance  of  the  earth 
and  moon  formed  a  gaseous  ring,  recently  parted  from 
the  rotating  nebula.  The  assigned  diameter  of  the 
ring  was  of  the  order  of  the  orbit  of  the  earth.  It  may 
help  to  an  appreciation  of  the  gravitative  feebleness  of 
this  ring,  to  note  that  even  if  it  were  reduced  to  a  solid 
state  of  the  mean  density  of  the  present  earth,  it  would 
have  a  cross-section  of  only  about  40  kilometers.  It 
is  further  to  be  noted  that  the  center  of  gravity  of  the 
ring  would  be  at  the  center  of  the  sun  and  the  self- 
gravity  of  any  section  of  the  ring  would  be  exceedingly 
feeble.  When  all  that  these  two  factors  imply  was  duly 
considered,  the  case  became  eminently  decisive.  A 
ring  of  gas,  such  as  the  Laplacian  hypothesis  postulates  as 
the  parent  of  the  earth,  with  a  temperature  high  enough 
to  keep  the  refractory  substances  that  make  up  most  of 
the  earth  in  the  form  of  a  gas,  could  not  have  held  itself 
together  by  its  own  gravity  in  the  collisional  relations  of  a 
gas,  most  certainly  not  so  far  as  the  atmospheric  con- 
stituents were  concerned. 

When,  therefore,  the  results  of  this  ultimate  test  had 
been  duly  pondered,  one  of  two  alternatives  seemed 
imperative:  either  to  conclude  that  the  kinetic  theory 
of  gases  was  seriously  wrong,  or  that  such  a  ring  of 
gas  as  the  Laplacian  hypothesis  postulated  could  not 
have  held  in  gaseous  relations  the  waters  of  the  oceans 
or  the  constituents  of  the  air,  nor  perhaps  even  the  rock 
substances  of  the  earth. 

At  the  time  the  test  was  made  there  was  ground  for 
some  reserve  relative  to  the  soundness  of  the  kinetic 
theory  of  gases.  It  seemed  wise,  therefore,  before 
setting  aside  the  Laplacian  hypothesis,  to  seek  lines  of 


THE  GASEOUS  THEORY  OF  EARTH-GENESIS     37 

test  that  did  not  rest  on  the  trustworthiness  of  the 
kinetic  theory  of  gases.  These  will  claim  attention  later. 
Before  passing  on,  however,  it  is  proper  to  remark  that 
there  now  remains  no  reasonable  ground  for  doubting 
the  essential  verity  of  the  kinetic  theory  of  gases. 
The  test  based  on  this  theory  was,  therefore,  really 
much  more  conclusive  than  it  was  held  to  be  at  the  time 
it  was  made. 

REFERENCES 

1.  T.  C.  Chamberlin,  "On  the  Bearing  of  Molecular  Activity  on  the 
Spontaneous  Fission  of  Gaseous  Spheroids,"   Carnegie  Institution    of 
Washington,  Publication  107  (1909),  pp.  161-67. 

2.  G.  Johnstone  Stoney,  "On  the  Cause  of  the  Absence  of  Hydrogen 
from  the  Earth's  Surface  and  of  Air  and  Water  from  the  Moon,"  Trans- 
actions of  the  Royal  Dublin  Society,   1892;    "On  Atmospheres  upon 
Planets  and  Satellites,"  ibid.,  1897;  ibid.t  1898,  p.  305;  "On  the  Pres- 
ence of  Helium  in  the  Earth's  Atmosphere  and  Its  Relation  to  the 
Kinetic  Theory  of  Gases,"  Astrophysical  Journal,  VIII  (1898),  316. 

3.  S.  R.  Cook,  "On  the  Escape  of  Gases  from  Planetary  Atmospheres 
According  to  the  Kinetic  Theory,"  Astrophysical  Journal,  XI  (1900),  36; 
G.  Johnstone  Stoney,  "On  the  Escape  of  Gases  from  Planetary  Atmos- 
pheres According  to  the  Kinetic  Theory,"  No.  I,  ibid.,  XI  (1900),  151; 
No.  II,  ibid.,  XI  (1900),  325;   "Note  on  Inquiries  as  to  the  Escape  of 
Gases  from  Atmospheres,"  ibid.,  XII  (1900),  201. 

4.  T.  C.  Chamberlin,  "A  Group  of  Hypotheses  Bearing  on  Climatic 
Changes,"  Journal  of  Geology,  V  (1897),  653. 

5.  F.  R.  Moulton,  ibid.,  p.  659. 

6.  A.  W.  Whitney,  ibid.t  p.  661. 


CHAPTER  II 

VESTIGES  OF  COSMOGONIC  STATES  AND  THEIR 
SIGNIFICANCE 

There  was  a  time  when  that  part  of  the  history  of  the 
earth  which  antedates  human  records  was  held  to  be 
purely  speculative.  It  was  easy  to  say  that  no  man  had 
then  lived  to  witness  terrestrial  events  and  they  could 
not  be  humanly  known.  Pre-human  history  was,  indeed, 
merely  speculative  until  a  certain  stage  in  the  growth  of 
insight  had  been  reached.  Man  had  lacked  the 
acumen  to  read  the  record  written  in  the  earth  itself 
by  the  processes  of  its  own  formation.  Ignoring  this 
automatic  record,  he  indulged  in  speculative  fancies  in 
lieu  of  serious  inquiry.  But  he  has  since  learned  that 
the  automatic  vestiges  of  creation  may  be  read  with 
great  trustworthiness  so  far  as  their  larger  import  is 
concerned;  he  is  learning  almost  daily  of  successful 
advances  in  deciphering  the  less  readable  phases  of  the 
record.  It  is  not  unnatural  that  the  autobiography  of 
the  earth  should  vary  greatly  in  the  clearness  and 
cogency  of  its  revelations.  The  most  tangible  part 
of  the  record  is  found  in  material  vestiges,  in  footprints 
of  processes  and  footprints  of  living  creatures,  in  ripple 
marks,  in  mud-cracks,  in  fossils,  in  the  necks  of  decapi- 
tated volcanoes,  in  the  roots  of  vanished  mountains, 
and  in  the  multitude  of  distinctive  marks  left  by  former 
activities.  The  laying  down  of  the  strata  one  upon 
another  in  orderly  sequence — the  rings  of  terrestrial 

38 


VESTIGES  OF  COSMOGONIC  STATES  39 

growth — and  the  great  lines  of  the  earth's  architecture 
are  replete  with  historic  testimony  of  unimpeachable 
fidelity.  But  these  materialistic  records  are  by  no 
means  the  only  ones,  nor  always  the  most  important 
ones;  there  are  dynamic  relics  that  are  as  truly  vestiges 
of  processes  once  in  progress  as  are  fossils  or  strata. 
These  may  be  rotations,  revolutions,  inclinations  of 
axis,  ellipticities,  or  any  other  of  the  activities,  attitudes, 
or  configurations  that  make  up  the  subject-matter  of 
celestial  mechanics  and  of  terrestrial  dynamics.  These 
residual  activities,  attitudes,  and  configurations  may 
imply  past  events  as  specific  in  their  natures  and  as 
illuminating  in  their  historic  significance  as  those  more 
familiar  material  vestiges  of  earth-processes  by  which 
its  history  is  now  so  confidently  read.  The  testimony 
of  these  dynamic  vestiges  may  often  seem  to  be  more 
difficult  to  interpret  than  the  meaning  of  the  material 
vestiges.  To  many,  perhaps,  they  seem  more  elusive 
in  their  nature  and  less  cogent  in  their  significance,  but, 
in  some  instances,  and  in  some  respects  at  least,  the 
opposite  is  really  the  truth.  In  not  a  few  cases  the 
dynamic  testimony  is  singularly  convincing.  Dynamic 
evidence  has  indeed  its  limitations,  as  have  all  kinds 
of  testimony,  but,  in  its  own  field,  it  is  often  surpassingly 
clear  and  altogether  decisive. 

As  the  history  of  the  earth  is  traced  back  to  those 
early  stages  in  which  its  substance  took  on  physical 
states  other  than  those  it  now  bears,  the  special  forms 
that  give  meaning  to  the  material  record  vanish,  and  little 
recourse  is  left  but  to  turn  to  the  dynamic  record  which, 
fortunately,  is  often  less  mutable,  under  the  vicissitudes 
that  affect  earth-substance.  The  method  of  inquiry, 


40  THE  ORIGIN  OF  THE  EARTH 

however,  remains  substantially  the  same.  The  progress 
of  inquiry  from  sole  reliance  on  human  records  to  the 
interpretation  of  the  testimony  of  the  rocks  was  not  a 
lapse  from  a  realm  of  determinate  certainty  to  a  realm  of 
equivocal  speculation,  as  some  laymen  were  wont  to  say 
when  earth-science  was  in  its  infancy;  nor  is  the  passage 
of  inquiry  from  the  use  of  material  records  to  the  study 
of  the  dynamic  record  a  plunge  from  firm  science  into 
nebulous  speculation,  as  some  devotees  of  science  permit 
themselves  to  hint  even  now;  it  is  merely  an  onward 
step  from  the  reading  of  the  more  tangible  and  the  easier 
to  the  reading  of  the  less  tangible  and  the  more  difficult. 
No  doubt  the  reading  of  the  easier  and  the  more  familiar 
is  to  be  received  with  greater  confidence,  for  the  time 
being,  than  the  reading  of  the  less  tangible  and  the  more 
difficult.  The  need  for  severe  scrutiny  before  acceptance 
is  without  doubt  more  Fmperative  in  dealing  with  the 
latter  than  with  the  former,  but  close  scrutiny  is  needed 
in  both  cases;  it  is  needed  always  and  everywhere.  The 
reading  of  the  later  history  of  the  earth  and  the  reading 
of  its  earliest  history  are  parts  of  the  same  endeavor  and 
proceed  by  similar  processes.  The  indispensable  factor 
in  both  cases  is  a  scrupulous  search  for  vestiges  of  what 
has  taken  place  and  a  studious  endeavor  to  find  the  inter- 
pretation thereof. 

THE   VESTIGES   IX   THE   SUN 

When,  as  stated  near  the  close  of  the  last  chapter,  the 
atmospheric  test  of  the  Laplacian  view  of  the  origin  of  the 
earth  seemed  to  give  results  seriously  adverse  to  that 
hypothesis  and  to  make  it  wise  to  test,  in  turn,  the 
trustworthiness  of  this  test  itself  by  finding  some  other 


VESTIGES  OF  COSMOGONIC  STATES  41 

mode  of  scrutiny  free  from  dependence  on  the  theory  of 
gases,  attention  happened  to  be  first  drawn  to  the  slow- 
ness of  the  sun's  present  rotation.  This  rotation  is  an 
inheritance  from  the  rotation  the  sun  had  when  the 
planets  were  formed,  and  is  as  truly  a  vestige  of  creation 
as  the  Silurian  formations,  the  Cambrian  trilobites,  or  the 
Paleozoic  Alps.  Attention  was  later  directed  to  the 
obliquity  of  the  sun's  axis,  another  dynamic  vestige  of 
like  fundamental  nature. 

It  is  one  of  the  basal  postulates  of  the  Laplacian 
hypothesis — and,  substantially,  of  all  other  hypotheses 
that  belong  to  the  same  genus — that  the  nebula  which 
evolved  into  the  solar  family  had  a  certain  rotation  when 
it  was  in  its  most  expanded  condition,  and  that,  as  it 
cooled  and  shrank,  its  rate  of  rotation  increased  in 
accordance  with  mechanical  law  to  preserve  the  value 
of  its  rotatory  momentum,  technically  its  moment  of 
momentum.  The  constancy  of  the  moment  of  momen- 
tum in  such  a  rotatory  system  is  one  of  the  best  estab- 
lished principles  of  mechanics.  It  is  inevitably  involved 
in  all  centrifugal  theories  of  celestial  genesis,  and  must 
indeed  enter  radically  and  consistently  into  any  cos- 
mogonic  theory,  whatever  its  nature,  if  such  theory  is  to 
have  any  claim  to  serious  consideration.  As  such 
indispensable  principle,  it  is  susceptible  of  being  made  a 
criterion  of  the  highest  value  in  testing  the  validity  of 
cosmogonic  tenets.  It  is  peculiarly  applicable  to  the 
tenets  of  hypotheses  confessedly  founded  on  it.  In 
the  application  of  this  principle,  it  was  held  under  the 
Laplacian  hypothesis — by  implication,  if  not  by  open 
declaration — that  when  the  parent  nebula  by  cooling  had 
shrunk  to  a  diameter  of  about  five  and  one-half  billion 


42  THE  ORIGIN  OF  THE  EARTH 

miles — the  velocity  at  its  equator  being  then  three  and 
four-tenths  miles  per  second — a  ring  was  separated  by 
centrifugal  action  which  afterward  gathered  into  the 
planet  Neptune.  When,  two  stages  later,  the  nebula 
had  shrunk  to  a  diameter  somewhat  less  than  a  billion 
miles — the  velocity  then  acquired  being  about  eight 
miles  per  second  at  the  equator — a  more  massive  ring 
was  supposed  to  have  been  separated  which  later  formed 
the  great  planet  Jupiter.  When,  again  omitting  two 
stages,  the  nebula  had  shrunk  to  a  diameter  about  equal 
to  that  of  the  orbit  of  the  earth — its  equatorial  velocity 
having  risen  to  eighteen  and  a  half  miles  per  second— 
another  ring  was  separated  which  formed  the  earth. 
When  the  nebula  had  shrunk  to  a  size  comparable  to  the 
orbit  of  Mercury,  its  equatorial  speed  had  risen  to  about 
twenty-nine  miles  per  second.  As  shrinkage  con- 
tinued after  the  separation  of  Mercury,  the  principle 
requires  that  proportionate  increases  of  rotatory  velocity 
should  have  ensued.  Further  separations  of  equatorial 
matter  and  further  formation  of  planets  might,  in 
complete  consistency  with  the  hypothesis,  be  presumed 
to  have  taken  place  and,  indeed,  were  presumed  to  have 
taken  place  by  the  astronomers  of  the  last  century. 
They  made  diligent  search  for  inner  planets  at  times  of 
solar  eclipse  when  the  glare  of  the  sun,  that  might  ordi- 
narily obscure  small  planets  in  its  vicinity,  was  cut  off. 
An  eminent  astronomer  even  announced  the  discovery  of 
such  a  planet  and  named  it  Vulcan,  but  the  observation 
proved  illusory.  Now,  if  Vulcan  had  proved  to  be  a 
reality,  and  if  the  radius  of  its  orbit  had  been  a  million 
miles,  its  velocity  in  its  orbit,  if  circular,  should  have 
been  about  170  miles  per  second,  and  the  equatorial 


VESTIGES  OF  COSMOGONIC  STATES  43 

velocity  of  rotation  of  the  parent  nebula  at  the  time  of 
the  planet's  supposed  separation  should  have  been  the 
same.  The  further  contraction  of  the  nebula  to  the 
present  radius  of  the  sun  should  have  given  it  an  equa- 
torial velocity  of  270  miles  (435  kilometers)  per  second. 
But  the  actual  velocity  of  the  sun's  equator  is  only  about 
one  and  a  third  miles  (two  kilometers)  per  second.  In 
other  words,  the  actual  velocity  is  only  about  one-half  of 
i  per  cent  of  the  theoretical  requirement.  Here  then  is 
an  enormous  discrepancy.  The  discrepancy  is  the 
more  notable  in  that  it  arises  from  the  very  principle  on 
which  the  hypothesis  is  founded.  Interpreted  as  a 
dynamic  relic  of  the  sun's  past  history  and  as  an  index 
of  its  genesis,  this  inconsistently  slow  rotation  seems  to 
imply  that  the  sun  is  not  the  residual  product  of  any  such 
a  system  of  progressive  separations  as  the  Laplacian  and 
similar  centrifugal  hypotheses  postulate.  It  is  not 
easy  to  see  how  this  conclusion  can  be  escaped,  unless 
it  can  be  shown  that  some  competent  agency,  acting  as  a 
break,  came  into  action  after  the  separation  of  Mercury 
and  was  efficient  enough  to  reduce  the  rotation  of  the 
sun  to  a  two-hundredth  part  of  the  velocity  toward  which 
it  had  been  trending  up  to  this  stage  in  accordance  with 
one  of  the  best  established  laws  of  mechanics.  There 
is  an  inherent  difficulty  in  seeing  just  how  any  such 
agency,  or  the  source  of  any  such  agency,  could  have 
existed  in  the  system  and  have  remained  in  abeyance 
during  the  whole  active  period  of  planetary  evolution 
so  as  to  permit  rotation  to  increase  systematically  until 
all  the  planets  were  cast  off,  and  then,  but  then  only, 
have  come  into  action  of  an  opposite  order  and  of  so 
high  efficiency  that  further  contraction  should  not 


44  THE  ORIGIN  OF  THE  EARTH 

only  have  failed  to  sustain  the  previous  habit  of  steadily 
increasing  rotation  but  should  have  reversed  the  effect 
with  so  much  potency  as  to  bring  the  rotation  down  to  a 
very  small  fraction  of  what  had  already  been  attained. 
However,  a  possible  agency  working  somewhat  in  this 
strange  way  must  be  considered.  So  long  as  the 
planetary  matter  remained  in  the  form  of  rings,  its 
attraction  had  no  deterrent  action  on  the  sun's  rotation, 
but  as  soon  as  the  rings  were  gathered  into  concentrated 
masses,  as  the  hypothesis  assumes  they  did,  each  of 
these  masses  tended  to  develop  tides  in  the  sun,  and  these 
tides  acted  as  brakes  on  its  rotation.  Now,  in  the  first 
place,  it  must  be  noted  that  as  soon  as  any  planetary 
mass  began  to  act  in  this  way,  it  tended  to  stop  the 
planet-forming  process.  Too  much  efficiency  of  this 
kind  on  the  part  of  the  outer  planets  would  have  fore- 
stalled the  formation  of  the  inner  planets.  Now  the 
time  at  which  such  masses  could  be  most  effective  was 
in  their  earliest  stages,  for  then  the  solar  body  was 
largest  and  its  proximate  side  was  nearest  to  them  while 
its  distal  side  was  farthest  from  them.  Furthermore,  the 
tides  of  these  first-formed  masses  were  then  least  neutral- 
ized by  the  tides  of  the  later-formed  masses.  The  planets 
are  distributed  about  the  sun  by  their  different  rates  of 
revolution  and  are  rarely,  if  ever,  all  on  a  single  side  of  the 
sun,  or  on  the  opposite  sides,  so  as  to  conjoin  their  tidal 
effects.  Their  distribution  is  constantly  changing,  so 
that  any  distribution  that  tends  to  tidal  efficiency  is 
merely  temporary.  As  a  result,  their  several  tides 
neutralize  one  another  in  large  degree  and  the  residual 
effect  is  small.  The  subject  of  tidal  influence  in  the 
evolution  of  our  planetary  system  has  been  elaborately 


VESTIGES  OF  COSMOGONIC  STATES  45 

investigated  by  Sir  George  Darwin,  and  as  his  working 
hypotheses  were  such  as  to  give  to  tidal  effects  their 
maximum  probable  values,  his  results  are  assumed  to 
be  conclusive.  He  found  that  the  utmost  assignable 
effects  of  all  the  planetary  tides  upon  the  rotation  of  the 
sun,  and  upon  the  reciprocal  retreat  of  the  planets,  is  so 
trivial  as  to  be  quite  negligible.  Even  if  the  age  of  the 
system  be  greatly  extended  beyond  current  estimates,  the 
evolutionary  value  of  the  planetary  tides  does  not  rise 
to  appreciable  moment.1 

As  the  sun  is  constantly  radiating  away  enormous 
quantities  of  heat,  it  is  improbable  that  the  retarding 
action  of  the  planetary  tides  has  been  at  any  time 
equal  to  the  accelerating  effect  of  the  sun's  contraction, 
even  if  the  solar  contraction  is  much  slower  than  was 
formerly  supposed,  owing  to  sources  of  heat  then 
undiscovered.  It  is,  however,  impracticable  to  deter- 
mine this  positively  in  the  present  state  of  knowledge 
relative  to  the  sun's  sources  of  heat. 

If  there  were  any  doubt  as  to  the  incompetency  of  the 
planetary  tides  to  account  for  the  great  discrepancy 
between  the  actual  rotation  of  the  sun  and  the  theoretical 
rotation  it  should  have  under  the  Laplacian  hypothesis, 
this  doubt  should  prompt  us  to  a  search  for  other 
grounds  on  which  to  test  the  hypothesis  by  the  applica- 
tion of  fundamental  principles,  for  discrepancies  are 
almost  sure  to  insinuate  themselves,  under  the  mantle 
of  any  hypothesis  that  does  not  tally  with  the  historic 
reality.  While  no  doubt  is  here  entertained  as  to  the 
incompetency  of  tidal  action  to  explain  the  great  dis- 
crepancy disclosed  by  the  rotation  of  the  sun,  an  inde- 
pendent line  of  inquiry,  undertaken  to  cover,  so  far 


46  THE  ORIGIN  OF  THE  EARTH 

as  possible,  any  weaknesses  that  might  be  supposed 
to  lurk  in  this  argument  and  in  the  preceding  atmospheric 
test,  will  be  the  subject  of  the  next  chapter.2 

It  was  only  after  such  a  supplementary  inquiry  had 
been  made  that  the  implications  of  the  second  of  the 
sun's  significant  vestiges,  the  inclination  of  its  axis 
to  the  planes  of  the  planets,  arrested  serious  attention, 
and  so,  if  strict  historic  sequence  were  followed,  this 
feature  should  be  discussed  later;  but  while  we  are 
considering  the  dynamic  vestiges  of  the  sun,  it  is  con- 
venient to  refer  briefly  to  the  inclination  of  its  axis. 
It  must  be  quite  obvious  to  everyone  familiar  with 
ordinary  mechanics  that,  if  the  sun,  by  reason  of  its 
rotation,  "threw  off"  parts  of  itself  by  centrifugal 
action,  they  should  have  taken  paths  lying  in  the  plane 
of  its  equator;  much  more  is  this  evident  if  the  center 
of  the  nebula  simply  shrank  away  from  the  outer  rim, 
the  true  picture.  This  holds  whether  these  parts 
were  left  behind  as  rings  or  as  individual  particles,  or  in 
any  other  natural  manner. 

But  as  a  matter  of  fact  the  plane  of  the  earth's  orbit 
is  inclined  7°  15'  to  the  plane  of  the  sun's  equator.  The 
orbits  of  all  other  planets  are  also  inclined  to  the  plane 
of  the  sun's  equator,  some  more,  some  less  than  this; 
some  of  the  planetoids  very  much  more  than  this.  If, 
however,  these  varying  inclinations  were  such  as  com- 
pletely to  offset  one  another  so  that  the  mean  plane 
coincided  with  the  sun's  equator,  the  conditions  of  the 
theory  might  still  be  regarded  as  fulfilled;  but  the 
"invariable  plane"  of  the  planetary  system  which  sum- 
marizes the  total  inclination  values  of  all  the  planetary 
orbits  is  also  inclined  to  the  sun's  equator  5°=*=.  While 


VESTIGES  OF  COSMOGONIC  STATES  47 

this  is  not  a  very  large  angle,  the  inertia  represented 
by  the  motion  of  the  planets  is  so  enormous  that  even 
this  small  deviation  represents  a  rather  grave  dis- 
crepancy between  theory  and  fact,  though  it  does  not 
rise  to  the  serious  nature  of  the  preceding  discrepancy. 
It  will  be  necessary  to  recur  to  this  feature  when  later 
we  turn  from  destructive  criticism  to  the  much  more 
difficult  task  of  constructing  a  hypothesis  to  meet,  if 
possible,  this  and  the  many  other  significant  features  of 
the  actual  system. 

REFERENCES 

i.  Sir  George  Darwin,  "On  the  Tidal  Friction  of  a  Planet  Surrounded 
by  Several  Satellites  and  on  the  Evolution  of  the  Solar  System,"  Philo- 
sophical Transactions  of  the  Royal  Society  of  London,  Part  II  (1881), 
pp.  4QI-53S- 

2.  T.  C.Chambcrlin,  F.R.Moulton,  C.S.Slichtcr,\V.  D.  MacMillan, 
Arthur  C.  Lunn,  Julius  SteigliU,  "The  Tidal  and  Other  Problems," 
Carnegie  Institution  of  Washington,  Publication  107  (1909). 


CHAPTER  III 

THE  DECISIVE  TESTIMONY  OF  CERTAIN   VESTIGES 
OF  THE  SOLAR  SYSTEM 

When,  as  recited  in  the  first  chapter,  the  gaseous 
factor  of  the  nebular  hypothesis  seemed  to  betray  serious 
weaknesses  under  the  tests  of  the  kinetic  theory  of 
gases  and  when,  as  recited  in  the  last  chapter,  the  cen- 
trifugal factor  seemed  to  disclo.se  even  more  serious 
incongruities  when  tested  by  the  hypothesis'  own 
fundamental  tenet,  there  arose  a  pressing  need  to  seek 
other  and,  if  possible,  more  rigorous  tests.  It  could  not 
be  lightly  assumed  that  a  hypothesis  which  had  been 
so  widely  accepted  for  a  century  was  thus  fatally  weak 
in  its  own  fundamentals.  It  was  more  natural  to 
assume  that  the  inquirer  had  himself  fallen  into  error 
or  misconception.  However,  the  call  to  proceed  till  the 
error  or  the  misconception,  wherever  it  lay,  should  be 
disclosed  was  none  the  less  imperative.  The  call  was 
jKThaps  all  the  more  urgent  because  the  weaknesses  of 
this,  the  leading  gaseous  hypothesis,  seemed  to  involve 
all  other  gaseous  hypotheses  as  well  as  all  quasi-gaseous 
hyjx)theses  and  perhaps  all  centrifugal  hypotheses. 
Indeed,  it  seemed  to  raise  doubt  as  to  the  possibility  of 
even  framing  any  centrifugal  hypothesis  that  could  fit 
the  facts  of  our  planetary  system.  This  does  not  of 
course  imply  that  some  other  planetary  system  might 
not  arise  from  centrifugal  separation,  but  merely  that 
our  planetary  system,  being  what  it  is,  did  not  arise  in 

that  way. 

48 


TESTIMONY  OF  VESTIGES  OF  SOLAR  SYSTEM  49 

Dr.  Moulton  had,  as  previously  stated,  furnished 
me  with  tables  and  formulas  of  parabolic  velocities  for  the 
earth,  under  different  conditions  of  volume  and  rotation, 
as  an  aid  in  the  gaseous  inquiry,  and  I  had  sought  his 
good  opinion  relative  to  the  significance  of  the  sun's 
slow  rotation.  He  was  now  good  enough  to  join  seri- 
ously in  the  inquiry  and  to  take  the  leadership  in  testing 
the  tenets  of  the  Laplacian  hypothesis  by  means  of  the 
laws  of  dynamics,  a  line  of  investigation  in  which  the 
skill  of  a  master  in  celestial  mechanics  carried  a  value 
of  the  highest  order.  The  new  tests  were  singularly 
fertile  in  disclosing  discrepancies.1 


SPECIFIC    DEFECTS    OF    THE    LAPLACIAN    HYPOTHESIS 

i.  For  a  first  trial,  the  nebula  postulated  by  the 
Laplacian  hypothesis  as  the  parent  of  the  solar  system 
was  restored  by  Dr.  Moulton  as  faithfully  as  possible  by 
a  theoretical  conversion  of  the  entire  mass  of  the  present 
system  into  gas  and  by  assigning  to  it  such  a  deploy- 
ment as  would  be  required  by  the  accepted  laws  of 
gaseous  distribution.  In  doing  this  he  endeavored  to 
give  the  hypothesis  the  benefit  of  every  doubt  and  to 
allow  a  liberal  margin  of  safety  in  every  case  of  quanti- 
tative uncertainty.  To  this  restored  nebula  he  assigned 
the  full  value  of  all  the  momentum  the  system  now 
possesses.  Comparison  was  then  made  between  this 
representative  nebula  and  the  actual  solar  system  in 
regard  to  the  respective  values  of  their  momenta.  These 
values  are  fundamental  in  nature  and  should  tally 
closely  with  one  another  if  the  Laplacian  hypothesis 
were  true. 


50  THE  ORKilN  OF  THE  EARTH 

The  first  stage  selected  for  comparison  was  naturally 
that  at  which  the  restored  nebula  had,  by  hy]x>thesis, 
shrunk  to  the  size  of  the  orbit  of  Neptune  and  was  ready 
to  cast  of!  a  ring  to  form  that  planet.  The  value  of  the 
momentum  in  the  nebula  and  the  value  of  the  momen- 
tum that  would  be  necessary  to  bring  about  the  separa- 
tion of  the  postulated  ring  by  centrifugal  action  were 
each  computed  and  were  found  to  be  widely  discrepant, 
the  momentum  of  the  nebula  having  less  than  a  two- 
hundredth  of  the  value  required  for  separation.  A 
similar  trial  was  made  at  the  stage  when  the  matter  for 
Jupiter  should  have  parted  from  the  nebula,  and  it 
was  found  that  the  nebula  then  had  less  than  a  hundred 
and  fortieth  of  the  momentum  required  to  separate  a 
ring.  At  the  stage  assigned  for  the  setting  off  of  the 
earth-moon  ring,  the  nebula  had  about  an  eighteen- 
hundredth  of  the  momentum  necessary.  At  the  Mercury 
stage,  it  had  about  a  twelve-hundredth.  It  will  be 
seen  that  these  arc  discrepancies  of  a  very  high  order  and 
are  quite  comparable  in  this  rcsjH-ct  to  the  discrepancy 
disclosed  by  the  sun's  slow  rotation. 

While  these  inquiries  of  Dr.  Moulton  were  entirely 
independent  of  previous  investigations  in  like  lines,  as 
was  natural  from  the  si>ccial  way  in  which  he  was  led 
to  make  them,  it  was  found  later  that  Babinet  had 
detected  discrepancies  of  the  same  type  many  years 
previously.1  Though  his  conclusions  had  been  reached 
in  a  somewhat  analogous  way,  the  methods  pursued 
were  not  identical.  It  does  not  appear  from  what  can 
now  be  learned  that  Babinet  pushed  his  inquiry  so  far  as 
to  become  convinced  that  the  discrepancies  were  fatal 
to  the  Laplacian  hypothesis.  On  the  contrary,  he 


TESTIMONY  OF  VESTIGES  OF  SOLAR  SYSTEM      51 

seems  to  have  regarded  the  incongruities  merely  as 
difficulties  which  must  be  met  in  some  way  by  the 
hypothesis  which  he  appears  to  have  continued  to  accept. 

2.  In  the  tests  of  Dr.  Moulton,  each  stage  in  the  evo- 
lution of  the  nebula  was  considered  by  itself,  such  masses 
as  had  been  separated  previously  to  form  planets  outside 
the  one  under  consideration  being  subtracted  from  the 
nebula,  following  in  this,  as  in  other  respects,  precisely 
the  terms  of  the  Laplacian  hypothesis.  Each  case  was 
thus,  in  some  sense,  an  independent  one.  To  apply  the 
test  in  a  somewhat  different  way,  it  was  assumed  that 
the  whole  mass  of  the  system  remained  in  the  nebula 
until  the  rate  of  its  rotation  became  sufficient  to  force 
the  separation  of  the  rim  as  a  ring  in  accordance  with 
the  assumptions  of  the  hypothesis.  It  was  found  that  the 
centrifugal  component  would  not  rise  to  equality  with 
the  centripetal  force  of  gravity  until  after  the  nebula 
had  shrunk  within  the  orbit  of  the  innermost  planet. 

As  all  these  tests  were  based  on  well-established 
dynamical  laws,  the  conclusions  could  not  fairly  be 
regarded  as  much  less  than  rigorous,  except  perhaps  in 
so  far  as  they  were  dependent  on  the  accuracy  of  the 
restoration  of  the  nebula,  which  was  guided  by  the 
accepted  law  of  distribution  of  gases.  This  law,  while 
probably  rigorous  under  ideal  conditions,  shows  some 
tendency  to  break  down  in  cases  where  the  state  of  the 
gas  is  near  the  border  line  that  marks  the  transition  from 
the  gaseous  state  to  some  other  state;  but  in  all  known 
cases,  the  departures  from  the  strict  terms  of  the  law 
were  found  to  be  such  as  to  bear  against  the  hypothesis, 
so  that  here,  as  in  other  cases,  the  assumption  of  the 
complete  integrity  of  the  law  gave  the  hypothesis  the 


52  THE  ORIGIN  OF  THE  EARTH 

benefit  of  the  doubt.  The  critical  reader  will  readily 
see  that  the  true  law  of  distribution  might  vary  widely 
from  the  accepted  law  without  removing  in  any  large 
measure  the  great  discrepancies  disclosed. 

3.  Although  there  was  thus  no  tangible  ground  for 
apprehending  that  any  falling  away  from  the  law  of 
distribution  of  gases  could  essentially  weaken  the  rigor 
of  the  conclusions  reached  by  Moulton's  dynamical 
inspection,  it  seemed  none  the  less  desirable  to  find 
a  test  whose  working  factors  were  not  derived  from  the 
law  of  distribution  of  gases,  and  thus  cover  by  such 
alternative  inquiry  any  doubt  that  might  seem  to  arise 
from  this  source.  I  endeavored  to  find  such  a  test  in  a 
comparison  of  masses  and  momenta  as  they  now  exist.1 
The  method  proceeded  on  the  assumption  that  the 
masses  and  the  momenta  alike  remained  essentially 
constant  throughout  the  evolution,  an  assumption 
inherent  in  the  principles  of  the  Laplacian  hypothesis. 
Exchange  of  momentum  between  the  members  of  the 
system  is  not,  however,  excluded,  and  there  will  be 
something  to  say  of  the  possible  extent  of  this  after 
the  mode  of  trial  and  its  results  have  been  outlined. 
The  method  may  be  concretely  illustrated  in  the  case 
of  the  great  planet  Jupiter  which  fairly  represents  the 
general  tenor  of  the  results  in  other  cases.  Jupiter, 
including  his  satellites,  now  carries  a  little  less  than 
one-thousandth  (1/1,024)  of  the  mass  of  the  solar  system 
exclusive  of  the  planets  outside  Jupiter  which  do  not 
enter  into  this  comparison.  The  mass  of  the  nebula 
just  before  the  Jovian  ring  was  separated  from  it,  was, 
according  to  the  Laplacian  hypothesis,  identical  with 
the  combined  masses  of  Jupiter  and  the  bodies  within 


TESTIMONY  OF  VESTIGES  OF  SOLAR  SYSTEM  53 

its  orbit.  For  the  purposes  of  the  inspection  the 
momentum  values  now  carried  by  the  Jovian  family 
and  the  bodies  within  were  taken  from  the  computa- 
tions of  Sir  George  Darwin  and  thus  the  results  were 
made  to  rest  on  authoritative  data  wholly  independent 
of  the  computations  of  my  colleague.  Now  the  reader 
will  find  little  difficulty  in  forming  a  mental  picture 
that  roughly  represents  the  proportions  of  momentum 
and  of  mass  in  the  different  parts  of  a  symmetrical 
rotating  body  such  as  the  nebula  must  have  been;  at 
least  he  can  picture  disproportions  in  the  different 
parts  so  great  that  they  would  not  be  developed  in  a 
natural  evolution,  and  so  he  may  limit  to  his  own  satis- 
faction the  range  within  which  the  true  case  must  lie, 
without  assuming  to  know  precisely  what  the  exact 
fact  is.  If  skilled  in  mechanics,  he  may  use  a  series 
of  hypotheses  that  fix  more  definitely  the  range  within 
which  the  true  case  must  fall.  The  nebula  at  the  initial 
stage  of  partition  must  have  formed  an  oblate  spheroid 
rotating  at  such  a  rate  that  the  outer  one- thousandth 
part  was  just  ready  to  separate  to  form  Jupiter  and  his 
moons.  The  next  thousandth  part  lay  just  inside  that 
and  was  rotating  at  a  proportional  rate,  which  was 
somewhat  slower;  the  next  thousandth  lay  next  within 
and  was  still  slower,  and  so  on  down  to  the  last  thou- 
sandth which  had  almost  no  rotatory  momentum  at  all. 
The  value  of  the  momentum  in  each  case  is  measured 
by  the  product  of  the  mass,  the  speed,  and  the  length 
of  the  arm  on  which  each  part  was  rotating,  and  the 
comparison  is  to  be  between  the  outer  thousandth  and 
the  sum  of  all  the  remaining  nine  hundred  and  ninety- 
nine  thousandths.  If  the  reader  has  fixed  upon  the 


54  THE  ORIGIN  OF  THE  EARTH 

highest  proportion  of  the  total  momentum  that  could 
possibly,  in  his  judgment,  be  carried  by  the  outer  one- 
thousandth  part  of  the  nebula,  he  will  be  prepared  to 
appreciate  how  far  the  hypothesis  is  credible  when,  by 
recourse  to  the  data  of  Sir  George  Darwin,  it  is  found  that 
Jupiter  and  his  moons  now  earn-  96  per  cent  of  the  whole 
momentum,  leaving  to  the  remaining  nine  hundred  and 
ninety-nine  parts  only  4  per  cent.  In  some  respects 
this  remarkable  disproportion  is  quite  as  convincing 
evidence  that  Jupiter  was  not  separated  by  simple 
centrifugal  action  as  the  more  rigorous  determination  by 
the  previous  method  which  showed  that  the  existing 
momentum  is  one  hundred  and  forty  times  more  than 
the  same  matter  would  have  carried  in  the  restored 
nebula. 

When  this  alternative  method  was  applied  to  other 
planets,  similar  disproportions  between  masses  and 
momenta  were  disclosed;  in  some  cases  even  a  greater 
relative  disproportion  was  revealed  than  in  the  case 
of  Jupiter. 

4.  Inspections  of  the  foregoing  kinds  that  direct 
specific  attention  to  the  conditions  under  which  separa- 
tion should  take  place  force  the  conviction  that  a  certain 
regularity  and  symmetry  in  resj>ect  to  the  masses  of  the 
successive  rings  must  have  resulted  from  the  centrifugal 
process,  if  it  obtained.  But  very  striking  irregularities 
in  the  masses  of  the  planets  are  observed.  If  the  mass 
of  the  earth  be  taken  as  unity,  the  order  of  the  planetary 
masses  from  the  outermost  to  the  innermost  is  17; 
14.6;  94.8;  317.7;  0.1073;  i;  0.82;  0.0476.  This 
irregularity  has  of  course  long  been  known  and  the 
incongruity  recognized  but  not  thought  fatal. 


TESTIMONY  OF  VESTIGES  OF  SOLAR  SYSTEM   55 

5.  Rings  shed  from  the  rim  of  a  rotating  spheroid 
should  have  been  strictly  circular  when  they  were  first 
formed,  and  no  wide  departures  from  circularity  should 
probably  have  followed  in   the  course  of  subsequent 
evolution.     The  orbits  of  most  of  the  planets  approach 
fairly  closely  to  circularity  and  no  severe  indictment  of 
centrifugal  hypotheses  can  be  based  on  the  ellipticities 
observed,    though   some   of   them   are   rather   notable. 
The  orbits  of  the  planetoids,  however,  are  often  much 
more  eccentric,  and  their  planes  diverge  more  notably 
from  the  invariable  plane  of  the  system.     The  attraction 
of  their  powerful  neighbor  Jupiter  is  sometimes  held 
responsible  for  this.     There  is,  however,  a  singular  fact 
about  the  orbits  of  the  planetoids  that  is  not  met  by 
this  plausible  hypothesis.     Bodies  shed  from  a  nebula 
by  centrifugal  action  should  have  orbits  strictly  con- 
centric with  one  another;   no  orbit  should  loop  through 
any  other.     The  orbits  of  the  planetoids,  however,  are 
so  singularly  interlooped  that,  if  they  were  solid  rods, 
the  lifting  of  one  would  lift  the  whole  group. 

6.  If  we  turn  to  the  supposed  evolution  of  the  satel- 
lites   from    the    planets    by    centrifugal    action,    some 
features  as  strikingly  incongruous  as  any  of  the  preced- 
ing are  encountered.     Under  the  centrifugal  theory,  all 
the  satellite  rings  should  have  rotated  precisely  as  their 
parent  nebulae  did,  and  when  the  rings  were  condensed 
into  satellites  these  should  have  revolved  in  the  same 
direction  as  their  primaries.     Each  inner  ring  should 
have  rotated  in  less  time  than  the  rings  outside  it,  while 
the  central  body  should  have  rotated  in  a  shorter  period 
than  any  ring.     The  principle  is  the  same  as  that  already 
considered  in  relation  to  the  rotation  of  the  sun.     But 


56  THE  ORIGIN  OF  THE  EARTH 

Phobos,  the  inner  satellite  of  Mars,  revolves  around  that 
planet  more  than  three  times  while  the  planet  rotates 
once.  This  is  a  very  singular,  telltale  vestige  of  Mars's 
early  history.  While  this  anomaly  has  been  known 
ever  since  Hall  discovered  the  satellites  in  1868,  and 
has  been  recognized  as  puz/ling,  its  force  was  largely 
avoided  or  palliated  by  the  hypothesis  that  the  rotation 
of  Mars  was  indeed  high  at  the  outset  but  has  been  so 
reduced  in  the  course  of  time  by  the  tidal  action  of  its 
moons  that  the  present  strange  state  of  affairs  was 
reached.  Nolan,  however,  insisted  that  this  explanation 
was  inadequate.4  Moulton  added  piquancy  to  the 
anomaly  by  pointing  out  that  the  little  bcxlies  which 
make  up  the  inner  border  of  Saturn's  innermost  ring 
revolve  in  a  period  only  about  half  that  of  Saturn's 
rotation.  Moulton  further  pointed  out  that,  even  if  a 
tidal  scheme  could  be  made  to  fit  the  case  of  Mars, 
it  would  not,  at  the  same  time,  lit  the  case  of  Saturn, 
unless  it  were  assumed  that  Saturn  is  something  like 
three  thousand  times  as  old  as  Mars. 

7.  Though  it  is  not  in  proper  historical  order  here, 
this  is  a  convenient  place  to  remark  that  three  even 
more  telltale  cases  of  strange  behavior  on  the  part  of 
satellites  have  been  discovered  since  we  were  led  by  the 
foregoing  and  other  considerations  to  abandon  the 
centrifugal  theory  of  satellite  origin  and  to  adopt  a  new 
one.  Among  the  new  satellites  that  have  been  dis- 
covered by  photography,  it  appears  that  Saturn  has  one 
and  Jupiter  has  two  that  revolve  in  a  retrograde  direction 
contrary  to  the  rest.  Nothing  would  seem  more  obvious 
than  that  a  planetary  spheroid,  rotating  so  fast  as  ot 
shed  a  series  of  rings  by  centrifugal  action  to  form 


TESTIMONY  OF  VESTIGES  OF  SOLAR  SYSTEM  57 

satellites,  should  impart  to  them  all  its  own  direction 
of  motion.  Such  a  result  is  so  obvious  that  it  was 
formerly  taught  that  a  single  exception  would  be 
absolutely  fatal  to  the  Laplacian  theory,  and  the  writer 
was  so  instructed  in  his  college  days.  It  now  appears 
that,  while  the  majority  of  the  satellites  revolve  in  the 
same  direction  as  their  primaries,  a  minority  take  the 
opposite  course,  and  that  these  contrary  habits  are 
found  in  the  same  family  of  moons  in  two  cases. 

8.  Among  the  older  objections  to  the  ring  theory  was 
the  inference  that  a  gaseous  spheroid  would  not  cast 
off  a  definite  ring,  even  if  its  rotation  were  so  increased 
that  separation  in  some  form  was  inevitable.  It  was 
felt  that  the  molecules  would  go  off  separately,  or  at 
the  most  in  small  groups,  and  that  such  small  separations 
would  follow  at  short  intervals,  so  that  the  whole  would 
form  a  disk  rather  than  a  series  of  distinct  rings.  The 
molecules  of  gases  are  held  together  by  gravity  in  spite 
of  a  tendency  to  fly  apart  by  reason  of  rebounds  from 
collisions  with  other  molecules,  and  hence  so  soon  as 
gravity  at  the  outermost  rim  of  the  rotating  nebula 
was  neutralized  by  the  increasing  centrifugal  force, 
the  molecules  should  have  gone  off  individually  into 
orbits.  There  was  no  agency  to  hold  them  back  until 
the  other  molecules  requisite  to  make  up  a  ring  great 
enough  to  form  a  planet  should  also  have  reached  the 
state  requiring  separation.  A  ring  of  sufficient  magni- 
tude to  form  the  greater  planets  should  have  had  some 
millions  of  miles  of  depth  and  the  differences  in  the 
ratio  of  rotation  to  gravity  in  its  outer  and  in  its  inner 
edges  respectively  should  have  been  rather  large.  This 
objection  is  so  obvious  that  some  surprise  may  naturally 


58  THE  ORIGIN  OF  THE  EARTH 

be  entertained  that  the  formation  of  rings  was  ever 
made  a  part  of  the  hypothesis.  There  seem  to  have 
been  two  reasons,  doubtless  seemingly  cogent  at  the 
time,  for  the  introduction  of  the  ring  feature. 

One  of  these  was  a  supposed  logical  necessity  to  meet 
the  facts  of  planetary  rotation.  All  the  rotations  of  the 
secondary  bodies  of  the  solar  system  were  in  the  same 
direction  as  their  primaries,  that  is  forward,  so  far  as 
known  when  the  Laplacian  hypothesis  was  framed.  It 
was  reasoned  that  if  a  ring  rotated  as  a  unit,  the  outer 
part  of  which  moves  faster  than  the  inner,  the  rotation 
of  the  globe  into  which  the  ring  gathered  would  also  be 
forward;  but  if,  on  the  other  hand,  the  ring  were  made 
up  of  small  bodies  revolving  independently,  the  inner 
bodies  in  this  case  moving  faster  than  the  outer,  as 
they  must,  the  rotation  of  the  resulting  globe  would  be 
in  the  opposite  or  retrograde  direction.  This  cogent 
logic  seemed  to  warn  everyone  away  from  any  theory 
that  started  with  particles  pursuing  independent  revolu- 
tions. To  all  such  hypotheses  it  seems  to  have  served  as 
a  lion  in  the  way,  effectually  warning  off  cosmogonic 
pilgrims.  The  warning  seems  to  have  been  religiously 
heeded  throughout  the  last  century.  The  question 
will  arise  later  whether  it  was  anything  more  than  the 
skin  of  a  lion,  but  let  that  pass  here. 

The  other  reason  was  naturalistic.  The  rings  of 
Saturn  were  very  naturally  thought  to  be  vestiges  of  the 
evolutionary  process,  and,  correctly  interpreted,  they 
were  certainly  entitled  to  be  so  regarded.  There  can  be 
little  doubt  that  they  were  really  the  foster-parents  of  the 
ring  theory.  In  Laplace's  time,  it  was  not  unnatural  to 
suppose  that  they  were  gaseous.  It  required  the  acumen 


TESTIMONY  OF  VESTIGES  OF  SOLAR  SYSTEM  59 

of  later  mathematics  and  the  analyzing  power  of  the 
spectroscope  to  prove  that  the  rings  are  in  reality  com- 
posed of  little  bodies  revolving  independently,  satel- 
litesimals,  if  you  please,  the  very  class  of  bodies  that 
were  supposed  to  give  rise  to  retrograde  rotations.  For 
a  hypothesis  built  up  so  naturally  in  response  to  the 
apparent  teachings  of  such  lovely  celestial  objects  as  the 
Saturnian  rings  to  find  at  length  that  it  was  the  victim 
of  misplaced  confidence  was  indeed  a  cruel  fate. 

9.  But  our  study  of  the  case  did  not  leave  the  issue 
simply  with  the  conviction  that  the  rim  of  the  nebula 
would  separate  continuously  into  a  disk ;  it  went  farther 
and  raised  two  much  more  radical  questions,  the  first, 
whether  the  passing  off  of  the  molecules  individually 
would  not  forestall  the  state  at  which  the  centripetal 
force  of  gravity  would  be  overtaken  by  the  centrifugal 
force  of  rotation;  the  second,  whether  the  molecular 
orbits  would  really  be  circular,  as  assumed,  or  whether 
on  the  contrary,  they  would  not  be  so  far  elliptical  as  to* 
vitiate  the  reasoning  by  which  the  rings  were  regarded 
as  logically  necessary. 

In  the  first  chapter,  the  way  in  which  the  common 
collisional  atmosphere  passes  into  an  ultra-atmosphere 
of  vaulting  molecules,  and  the  way  in  which  a  part  of 
these  vaulting  molecules  pass  into  an  ultra-atmosphere 
of  molecules  in  orbital  flights,  were  set  forth.  Now  it  is 
clear  that  centrifugal  action  aids  the  passage  of  the 
collisional  molecules  into  vaulting  molecules  and  also 
aids  the  passage  of  some  of  these  vaulting  molecules 
into  orbital  molecules.  Every  increase  of  rotation,  by 
increasing  the  centrifugal  tendency,  increases  the  trans- 
fer of  molecules  from  the  collisional  to  the  vaulting  and 


6o  THE  ORIGIN  OF  THE  EARTH 

from  the  vaulting  to  the  orbital  states.  This  transfer 
is  at  the  expense  of  the  momentum  of  the  rotating  body, 
for  the  orbital  molecules  require  a  higher  mean  value  of 
momentum  than  the  mean  value  of  the  momentum  of  the 
molecules  of  the  collisional  atmosphere.  If  the  process 
is  closely  followed,  it  will  be  seen  that  as  the  centrifugal 
tendency  increases  almost  to  equality  with  the  opposing 
centripetal  force  of  gravity,  the  number  of  molecules  that 
are  driven  by  collisions  into  vaulting  leaps  and  orbits 
is  increased.  The  momentum  requisite  for  the  orbital 
movements  is  taken  from  the  molecules  from  which  the 
last  leaps  were  taken.  The  loss  of  these  molecules 
is  equated  later  with  the  rest  of  the  nebula.  The  infer- 
ence from  this  is  that  increase  of  rotation,  in  such  a  body, 
necessarily  finds  issue  in  increasing  the  number  of  mole- 
cules that  pass  into  orbits,  and  that  the  nebula,  because 
of  its  constant  loss  of  momentum,  would  never  reach 
the  state  at  which  molecules  will  be  separated  simply  by 
centrifugal  action;  they  would  rather  be  separated  by 
molecular  activity  superposed  on  the  high  rate  of  rotation 
attained.5  If  this  seems  a  too  subtle  distinction,  it  is  to 
be  observed  that  the  molecules  which  go  of!  through 
molecular  activity  pursue  orbits  that  have  a  great 
variety  of  eccentricities  so  that  their  subsequent  aggre- 
gation into  planets  and  satellites  is  conditioned  by  these 
eccentric  orbits  and  is  not  amenable  to  the  logical 
deduction  relative  to  rotation  cited  above  as  playing 
so  important  a  part  in  cosmogonic  thinking  for  the  past 
century.  Reference  must  be  made  to  a  later  discussion 
on  rotation  for  the  full  meaning  of  the  distinction  between 
aggregation  from  circular  concentric  orbits  and  aggre- 
gation from  heterogeneous  elliptical  orbits  respectively. 


TESTIMONY  OF  VESTIGES  OF  SOLAR  SYSTEM   61 

10.  Moulton  has  shown  that,  even  if  a  ring  were 
formed,  the  breaking  of  this  ring  at  some  weak  point 
and  the  collection  of  the  whole  into  a  globe,  as  postulated 
in  the  Laplacian  hypothesis,  if  it  does  not  traverse  the 
laws  of  celestial  mechanics,  is  at  least  attended  with 
grave  difficulties.  Even  if  a  large  nucleus  were  formed 
at  some  point  on  the  ring  to  serve  as  a  collecting  center, 
it  probably  could  not  gather  to  itself  bodies  in  inde- 
pendent circular  orbits  from  an  angular  distance  of 
more  than  60°  without  the  co-operation  of  some  other 
agency.  The  considerations  in  this  case  are  too  techni- 
cal to  be  introduced  here.  So  also  are  some  other 
criteria  developed  by  Dr.  Moulton  in  the  course  of  his 
inquiry. 

If  then  the  probabilities  are  strongly  against  the 
formation  of  a  coherent  ring  by  centrifugal  action,  and 
if  such  a  ring,  granted  that  it  be  formed,  could  not  hold 
the  lighter  molecules  at  the  postulated  temperatures 
in  such  a  case  as  that  of  the  earth,  and  if,  in  addition, 
the  mechanical  difficulties  of  segregation  into  a  single 
spheroid  were  highly  adverse,  if  not  insurmountable, 
even  under  the  most  favorable  circumstances,  this  line 
of  genesis  offers  little  in  its  favor  to  offset  the  grave  in- 
congruities and  discrepancies  disclosed  in  the  mechanics 
of  the  system. 

It  would,  however,  no  doubt  leave  an  unfair  impres- 
sion of  the  hypothesis  of  Laplace,  and  of  its  unsurpassed 
simplicity  and  beauty,  and  of  the  great  service  it  has 
rendered  the  progress  of  thought,  if  there  were  no 
recognition  of  the  fact  that  there  is  a  long  list  of  general 
harmonies  between  the  salient  features  of  the  solar 
system  and  the  broader  terms  of  the  hypothesis.  On 


62  THE  ORIGIN  OF  THE  EARTH 

such  general  harmonies  the  hypothesis  was  founded, 
and  from  these,  it  gathered  to  itself  a  wide  adherence. 
All  this  was  meritorious  in  its  day.  It  was  only  by  the 
progress  of  discovery — to  which,  indeed,  it  had  itself 
made  noble  contributions — and  by  advance  in  analytical 
inquiry,  that  these  broader  harmonies  were  found  to  be 
merely  general,  while  specific  incongruities  of  a  grave 
nature  were  disclosed.  In  some  notable  measure, 
though  not  wholly,  these  incongruities  were  veiled  at 
the  time  the  hypothesis  was  given  to  the  world  by  the 
great  French  astronomer  and  mathematician. 

Before  passing  to  the  next  phase  of  our  inquiry,  a 
word  is  to  be  said  relative  to  some  of  the  cosmogonies 
that  preceded  the  admirably  specific  theory  of  Laplace. 
Only  general  reference  has  been  made  to  these  thus 
far  for  they  really  took  almost  no  part  in  the  inquiry. 
There  were  specific  reasons  for  this.  For  the  greater 
part,  they  had  not  been  worked  out  into  specific  details 
that  could  be  applied  closely  to  the  peculiar  dynamic 
features  of  the  earth  and  its  planetary  kin,  and,  for  this 
reason,  they  were  not  fitted  to  play  any  serious  part 
in  an  inquiry  that  tried  to  proceed  naturalistically  on  the 
specific  testimony  of  the  dynamic  vestiges  borne  by  the 
planets.  It  was  of  some  interest,  to  be  sure,  that  these 
general  cosmogonic  theories  were  more  or  less  sus- 
ceptible of  being  made  the  point  of  departure  for  some 
new  view  of  the  genesis  of  the  earth  that  was  specific, 
if  one  felt  that  the  facts  of  the  dynamic  record  made 
such  an  effort  promising.  But  the  views  actually 
offered  for  consideration  were,  in  general,  too  vague 
to  take  their  places  beside  the  clear  and  sharp  tenets  of 
the  Laplacian  hypothesis.  As  earlier  intimated,  the 


TESTIMONY  OF  VESTIGES  OF  SOLAR  SYSTEM  63 

Laplacian   hypothesis   stands   alone   among   the   older 
views  in  its  laudable  definiteness. 

THE   LESS   SPECIFIC   HYPOTHESES 

To  a  notable  extent,  though  not  universally,  the 
other  older  cosmogonic  theories  centered  on  the  pro- 
found problem  of  original  creation,  or,  at  least,  on  the 
primitive  state  of  celestial  matter.  Following  back  along 
the  line  of  terrestrial  evidence,  as  our  inquiry  did,  and 
clinging  as  closely  as  possible  to  the  evidence  of  the 
earth's  automatic  record,  it  would  have  been  an  unwar- 
ranted leap  into  the  depths  of  speculative  assumption 
to  have  presumed  that,  when  we  had  reached  the  stage 
of  planetary  genesis,  we  had  also  reached  the  beginning 
of  things.  Nothing  whatever  had  been  found  in  the 
record  to  imply  that  the  birth  of  the  earth  was  a  feature 
of  the  absolute  beginning  of  the  universe.  As  inti- 
mated already,  once  and  again,  there  seemed  no  ground 
to  assume  that  the  origin  of  the  earth  stood  as  the  only 
type  of  origin  of  secondaries  in  the  great  universe,  or 
that  it  was  a  part  of  primitive  creation,  however  natur- 
ally it  may  have  been  assumed  by  the  ancients  to  be 
a  creative  ultima  Thule.  There  had  not  even  appeared 
in  the  record  any  clear  evidence  that  there  was  a  primi- 
tive creation  ex  nihilo,  as  distinguished  from  an  indefinite 
backward  extension  of  cycles  of  celestial  evolution. 
The  trend  of  our  inquiry — a  trend  that  will  appear  even 
more  distinctly  in  its  later  stages — lay  rather  in  the 
latter  direction.  The  inquiry  had  been  leading — and 
it  continued  to  lead — step  by  step  to  the  impression 
that  the  creation  of  our  planetary  system  was  but  an 
incident  in  the  history  of  our  sun,  while  even  the  genesis 


64  THE  ORIGIN  OF  THE  EARTH 

of  the  sun  might  not  improbably  be  but  an  incident 
in  the  history  of  our  stellar  galaxy,  and  the  genesis  of 
that  perhaps  only  an  episode  in  the  evolution  of  the  real 
universe  that  undoubtedly  lies  chiefly  beyond  our  ken. 
It  appeared,  therefore,  that,  while  our  inquiry  might 
lead  on  ultimately  to  some  consideration  of  the  evolution 
of  our  stellar  galaxy,  and  to  the  modes  of  genesis  of  the 
stars  and  their  attendants— which,  springing  from  sur- 
passingly rich  resources  of  energy  and  activity,  might 
follow  many  different  lines — only  a  small  part  of  this 
broad  complex  problem  lay  within  the  specific  field  of 
our  inquiry.  This  fraction,  however  small  relative  to 
the  whole,  was  none  the  less  all  too  great  for  our  investi- 
gative resources. 

To  a  large  extent,  as  intimated,  the  older  cosmogonic 
views  centered  upon  the  speculative  concept  of  primeval 
chaos,  or  a  modified  view  of  it,  and  made  this  chaos  the 
initial  stage  of  stellar  history.  Under  this  assumption 
there  usually  lay  the  postulate  of  absolute  creation,  but 
this  was  not  always  the  case.  Creation  ex  nihilo  was 
accompanied,  or  followed,  putatively,  by  endowments 
of  energy,  activity,  and  the  various  properties  of  matter, 
and  these  led  on  to  a  series  of  events  which  brought  the 
sun  and  the  planets  into  being.  The  whole  solar  system 
was  thus  made  the  direct  offspring  of  a  primitive  series 
of  events.  The  sun  and  the  planets  were  assigned  a 
common  birth.  The  details  and  special  stages  were 
more  or  less  successive,  indeed,  but  the  whole  was  one 
great  unitary  evolution.  This  general  postulate  of  a 
common,  and  essentially  contemporaneous,  evolution  of 
sun,  stars,  planets,  and  satellites  was  a  feature  common 
to  most  of  the  older  cosmogonic  theories.  In  this  they 


TESTIMONY  OF  VESTIGES  OF  SOLAR  SYSTEM  65 

were  at  one  with  the  Laplacian  hypothesis.  A  departure 
from  this  prevailing  conception  appeared,  however,  in 
the  latter  part  of  the  eighteenth  century,  in  the 
collisional  hypothesis  of  Buffon.  To  this  we  shall  refer 
later. 

Where  primeval  chaos,  or  any  form  of  a  universal 
diffuse  condition  was  taken  as  the  original  state,  some 
form  of  segmentation  must  necessarily  have  followed  as 
a  means  by  which  appropriate  volumes  of  the  diffuse 
matter  came  to  be  separated  from  the  rest  in  a  form 
suited  to  gather  later  into  the  several  stellar  systems — 
the  solar  system  being  the  case  of  particular  interest 
to  us.  The  mechanics  assigned  for  such  a  segregation 
were  very  obscure,  or  altogether  neglected.  Even  the 
segregation  itself  was  passed  over  lightly.  If  original 
uniformity  was  assumed,  as  obscurely  implied  in  most 
cases,  as  definitely  stated  in  some,  the  assigned  agencies 
that  actuated  such  sub-segregation  rested  on  doubtful 
bases.  If  in  any  case  departure  from  original  uniformity 
was  implied,  no  specific  asymmetry  suited  to  produce 
just  the  right  kind  of  segregation  seems  to  have  been 
postulated  in  any  instance.  Such  dynamic  insight  was 
perhaps  more  than  could  be  expected  from  the  attain- 
ments of  the  earlier  ages  in  mega-mechanics. 

Passing  this  by,  the  dynamics  of  the  later  processes 
by  which  the  subdivisions  of  the  universal  chaos  gathered 
into  stars  and  planets  were  often  scarcely  less  obscure. 
When  definite,  they  were  usually  untenable. 

Aside  from  the  great  historical  interest  that  attaches 
to  these  earlier  attempts  at  the  solution  of  the  great 
problem  of  the  genesis  of  the  heavens  and  the  earth,  and 
apart  from  the  genuine  admiration  they  awaken  for  the 


66  THE  ORIGIN  OF  THE  EARTH 

ingenuity  and  breadth  of  view  some  of  them  display, 
notwithstanding  their  shortcomings,  only  one  among 
them  has  claimed  the  serious  attention  of  modern  scholars, 
the  Kantian  hypothesis,  and  that  not  very  widely.  If 
our  inquiry  had  been  a  study  in  general  cosmogony, 
instead  of  a  search  for  the  genesis  of  our  planet,  the  Kan- 
tian view  might  perhaps  have  had  certain  claims  to  take 
precedence  over  even  the  Laplacian  hypothesis,  for 
the  latter  purposely  stopped  short  of  a  comprehensive 
philosophical  view  of  celestial  evolution;  it  neglected  to 
assign  an  origin,  or  to  delineate  the  early  history,  of  the 
nebula  with  which  it  dealt;  it  started  with  an  assump- 
tion; it  simply  postulated  a  nebula  of  given  mass  and 
physical  state;  it  did  not.  even  by  speculative  hypothesis, 
connect  this  nebula  with  its  own  origin  or  antecedent 
history,  much  less  with  an  absolute  beginning,  or 
even  with  a  general  parental  state,  as  die!  the  Kantian 
hypothesis. 

""Unfortunately  the  Kantian  hypothesis  was  made  to 
rest  on  the  untenable  view  that  the  rotatory  momentum 
of  the  system  would  arise  inevitably  from  the  centrip- 
etal action  induced  by  gravity  and  the  reaction  of 
atomic  repellency.  Other  mechanical  infelicities  crept 
in  also.  These  inhibited  any  modern  building  on  the 
Kantian  basis,  unless  its  dynamic  foundations  were 
replaced  by  sound  tenets,  and  tenable  substitutes 
did  not  offer  themselves  that  were  not,  in  essence, 
abandonments  of  the  Kantian  concept.  It  has  been  seen 
that  the  rotatory  momentum  of  the  planetary  system 
is  not  only  a  very  radical,  but  a  very  discriminative, 
element  in  the  dynamic  constitution  of  the  solar  system. 
It  has  already  appeared  —and  the  observation  will  gain 


TESTIMONY  OF  VESTIGES  OF  SOLAR  SYSTEM  67 

in  force  as  study  proceeds — that  the  dynamic  endow- 
ments of  the  sun,  on  the  one  side,  and  of  the  planets,  on 
the  other,  are  in  such  striking  contrast  that  they  seem 
to  imply  that  these  two  sections  of  the  solar  system  had 
different  histories,  or,  at  least,  that  some  differentiating 
agency  entered  into  their  histories  in  such  a  way  as  to 
give  them  contrasted  and  incongruous  endowments  of 
momentum.  The  critical  considerations  that  grew 
out  of  a  study  of  these  differential  endowments,  far 
from  leading  back  toward  a  simple  evolution  from  a 
common  apportionment  of  primitive  chaos,  seemed  to 
point  quite  specifically  in  the  opposite  direction.  The 
observed  apportionments  of  mass  and  momentum  in 
the  solar  system  were  found  to  depart  widely  from  the 
apportionments  naturally  assignable  to  a  systematic 
mode  of  evolution  from  a  single  common  mass  segregated 
from  the  primitive  chaotic  universe.  The  Kantian 
hypothesis  seemed,  therefore,  so  completely  excluded, 
not  only  by  the  fallacious  mechanical  concept  on  which 
it  was  based,  but  also  by  its  evolutionary  unfitness  to 
meet  the  requirements  of  the  case,  that  it  held  out 
no  inducement  to  serious  consideration.  Even  if  its 
mechanistic  infelicities  could  be  replaced  by  sound  ones, 
it  was  obvious  that  it  would  encounter  at  once  the 
more  serious  of  the  difficulties  that  were  found  to  bar 
out  the  Laplacian  hypothesis.  Whatever  place,  there- 
fore, the  Kantian  views  may  be  entitled  to  hold  in 
general  cosmogony,  they  did  not  seem,  while  our  inquiry 
was  in  its  early  stages — still  less  do  they  now  seem- 
to  have  any  serious  claims  to  consideration  as  an  account 
of  the  way  the  earth  and  its  fellow-planets  came  to  be 
what  they  are. 


68  THE  ORIGIN  OF  THE  EARTH 

THE  CRITICAL  FEATURES  OF  OUR  PLANETARY  SYSTEM 

It  is  pleasant  now  to  turn  from  the  unwelcome  ta>k 
of  destructive  criticism,  however  unavoidable,  to  the 
story  of  constructive  effort,  to  an  endeavor  to  find 
the  physical  forebears  of  those  dynamic  features  of  our 
planetary  system  that  had  been  gathering  sharpness 
of  significance  as  the  inspection  incident  to  these  criti- 
cisms proceeded.  Let  us  review  them  hastily  then 
before  turning  to  the  constructive  efforts  to  which 
they  led. 

i.  It  is  to  be  noted  with  emphasis  that  our  planetary 
system  is  a  closely  appressed  disk  of  revolving  bodies 
centered  on  an  invariable  plane;  and  that  the  total 
mass  of  the  planets  is  very  small  (745)  relative  to  the 
mass  of  the  sun.  If  the  sun  and  the  planets  are  the 
divided  parts  of  a  common  nebula,  the  process  of  parti- 
tion must  have  been  such  as  to  realize  this  very  unequal 
division  in  this  very  specific  form.  Such  an  extreme 
inequality  of  partition  seems  improbable  from  any 
centrifugal  or  other  agency  acting  proportionately  on 
a  common  mass.  The  extreme  flatness  of  the  discoidal 
form  points  to  some  powerful  genetic  agency  competent 
to  enforce  upon  the  system  the  appressed  configuration 
it  still  bears.  This  might  well  have  proved  one  of  the 
strong  points  of  the  Laplacian  hypothesis  and  of  the 
whole  centrifugal  genus,  if  the  specific  details  had  not 
been  found  so  seriously  adverse;  for  a  swiftly  rotating 
attenuated  mass  should  give  a  narrow  discoidal  con- 
figuration to  a  planetary  system  derived  in  this  way. 
Heterogeneous  assemblages  of  scattered  matter  coming 
in  from  various  directions,  however,  seem  to  be  still 
more  effectively  barred  out  because  they  appear  to  be 


TESTIMONY  OF  VESTIGES  OF  SOLAR  SYSTEM  69 

unsuited  to  give  this  markedly  discoidal  configuration, 
and  this  singular  partition  of  material. 

2.  While  the  discoidal  form  shuts  out  a  large  group  of 
hypotheses,  the  departures  from  perfect  symmetry  in 
the  masses  and  in  the  arrangements  of  the  planets  are 
no  less  critical.     While  the  orbits  of  the  planets  are 
subcircular,   they  are  yet  notably  eccentric,   varying 
from  0.00684  to  0.20560;    while  the  eccentricities  of 
the  orbits  of  the  planetoids  vary  from  0.07631  to  o.  2228. 
The  inclinations  of  the  planes  of  the  planets  to  the  plane 
of  the  earth's  orbit  vary  from  above  7°  downward.    The 
orbital  planes  of  the  planetoids  are  notably  more  inclined, 
ranging  up  to  38°.    While  the  limitations  of  these  varia- 
tions betray  the  general  control  of  some  powerful  genetic 
agency   that  made   for  a  discoidal   form,   they  show 
equally  that  the  control  was  neither  wholly  complete  nor 
strictly  unified.    The  variations  imply  the  influences 
of  deviating  agencies,  but  only  agencies  of  such  minor 
efficiency  that  they  could  merely  superpose  small  diver- 
gencies upon  the  symmetry  induced  by  the  master  force. 

3.  Not  only  are  all  the  planes  of  the  orbits  of  the 
planets  and  planetoids  inclined  to  the  equator  of  the 
sun,  but  the  invariable  plane  of  the  planetary  system, 
a  dynamic  summation  of  the  planes  of  the  whole  planet- 
ary group,  is  inclined  to  the  plane  of  rotation  of  the  sun, 
though  the  sun  is  the  controlling  body  of  the  system  in  a 
gravitative  sense.    This  inclination  is  not  great  enough 
in  itself  to  be  very  impressive,  but  it  falls  in  with  the 
other  vestiges  of  deviating  influence  and  adds  to  their 
significance.     The  inclination  of  the  sun's  plane  of  rota- 
tion gains  significance  when  it  is  recalled  that  it  affects 
744  of  the  745  parts  of  the  mass  of  the  system,  while 


70  THE  ORIGIN  OF  THE  EARTH 

the  several  divergent  planes  of  the  planets  taken  all 
together  affect  only  one  of  the  745  parts.  The  signifi- 
cance is  not  so  much  in  the  fact  that  there  is  variation 
in  the  inclination  of  the  planes  of  the  individual  planets 
from  that  of  the  controlling  body,  as  that  their  composite 
value,  represented  by  the  invariable  plane  of  the  planet- 
ary system,  is  inclined. 

4.  The  central  controlling  body,   though  it  carries 
3J5   of  the  mass,  carries  less  than  2  per  cent  of  the 
revolutionary  momentum  of  the  system.    The  remain- 
ing 7  i  y  °f  the  mass,  in  the  form  of  the  planets  and  the 
satellites,  carries  above  98  per  cent  of  the  momentum.* 
This  disparity,  so  deadly,  it  would  seem,  to  all  centrifugal 
theories  of  genesis,  must  probably  prove  deadly  to  some 
or  all  of  such  other  theories  as  are  built  on  an  unsound 
dynamical  basis,  while  it  should  help  to  point  the  way 
to  a  tenable  theory.     It  is  a  severe  criterion ;  its  applica- 
tion may  be  expected  to  narrow  greatly  the  range  of 
permissible  theories. 

5.  The  directions  of  rotation  and  revolution,  which, 
when  the  fathers  of  cosmogonic  effort  gave  forth  their 
hypotheses,  were  all  of  one  sense,  so  far  as  then  known, 
have  been  found,  as  discovery  has  proceeded,  increasingly 
divergent,    discordant,    and    puzzling.     This    recently 
reached  an  extraordinary  climax  in  the  discovery  that, 
while  the  majority  of  the  moons  of  Jupiter  and  Saturn 
revolve    in    harmony    with    their    primaries,    a    small 
minority,  two  in  the  Jovian  family,  one  in  the  Saturnian, 
revolve  in  the  opposite  direction.    This  is  a  climacteric 
anomaly. 

*The  momenta  of  the  planetoids  are  not  here  included;  they  would 
somewhat  increase  the  disparity. 


TESTIMONY  OF  VESTIGES  OF  SOLAR  SYSTEM      71 

All  of  the  criteria  involved  in  these  singular  features 
must  be  met  by  any  hypothesis  that  is  entitled  to  be 
regarded  as  having  even  working  qualities;  they  must, 
of  course,  be  fully  met  by  the  true  theory,  as  well  as 
critical  features  that  have  not  been  cited.  The  list 
here  noted  falls  short  of  being  exhaustive,  but  even 
these  bring  into  view  a  series  of  criteria  whose  severe 
requirements  are  at  once  formidable  and  directive. 

REFERENCES 

1.  F.R.MouJton,"An  Attempt  to  Test  the  Nebular  Hypothesis  by  an 
Appeal  to  the  Laws  of  Dynamics,' '  Astrophysical  Journal,  (1900),  103-30. 

2.  M.  Babinet,  Complex  rendus,  LII  (1861),  481. 

3.  T.  C.  Chamberlin,  "An  Attempt  to  Test  the  Nebular  Hypothesis 
by  the  Relations  of  Masses  and  Momenta,"  Journal  of  Geology,  VIII, 
(1000),  58-73. 

4.  Nolan,  Nature,  XXXIV,  287. 

5.  T.  C.  Chamberlin,  "On  the  Bearing  of  Molecular  Activity  on  the 
Spontaneous   Fission  of  Gaseous  Spheroids,"  Carnegie  Institution  of 
Washington,  Publication  107  (1909),  pp.  161-67. 


CHAPTER  IV 
FUTILE  EFFORTS 

When  some  fundamental  faith  on  which  one  has  long 
rested  gives  way  beneath  him  and  he  finds  himself 
plunged  in  a  sea  of  doubt,  it  is  in  the  natural  order  of 
things  that  he  should  flounder  awhile  in  the  endeavor 
to  find  a  new  bottom  or  a  new  float.  His  stress  is  all 
the  more  keen  if  he  awakens  at  the  same  time  to  a  realiza- 
tion that  unconsciously  he  has  built  freely  upon  his 
faith  and  that  many  a  pet  edifice  must  go  to  wreck  if  the 
foundation  is  really  gone.  No  one  quite  realizes  how 
much  of  accepted  doctrines,  of  current  interpretations, 
and  of  working  assumptions  have  been  built  subcon- 
sciously upon  the  nebular  hypothesis  and  upon  the 
derivative  doctrine  of  a  gaseo-molten  earth.  Xo  small 
part  of  the  traditional  tenets  of  geology  are  imperiled  if 
the  gasco-molten  state  of  the  primitive  earth  is  really 
brought  into  question. 

While  there  was  only  partial  appreciation  of  this  at 
the  time,  it  was  felt  to  a  disturbing  degree.  At  first, 
however,  there  was  some  comfort  in  the  feeling  that 
there  were  many  alternatives  upon  which  it  was  easy 
to  fall  back  if  the  old  view  really  proved  untenable. 
If  the  earth  did  not  arise  from  a  gaseous  nebula  that 
shed  rings  to  form  planets,  it  seemed  a  light  matter  to 
shift  belief  to  an  origin  from  a  meteoritic  swarm  that 
masqueraded  as  a  nebula,  or  to  an  aggregation  of 
meteorites  gathering  in  from  the  four  quarters  of  the 

72 


FUTILE  EFFORTS  73 

heavens.  Perhaps  stars  might  collide  and  reform  into 
a  new  system,  or  nebulae  might  encounter  one  another 
and  start  a  special  evolution,  or  some  other  of  the  possible 
permutations  and  combinations  of  celestial  agencies 
might  have  functioned  in  a  genetic  way.  With  such  a 
plethora  of  alternatives  it  was  easy  to  persuade  one's  self 
that  our  geologic  tenets  might  be  transferred  to  some  new 
cosmogonic  base  and  still  be  entertained,  if  the  old 
foundation  could  carry  them  no  longer. 

And  yet  the  question  continued  to  rise  insistently: 
How  many  of  these  alternative  concepts  had  really 
escaped  the  stress  which  dynamical  laws  appeared  to 
put  on  the  most  symmetrical  and  complete  of  all  the 
inherited  hypotheses,  not  to  say  the  hypothesis  most 
honored  by  an  eminent  parentage  and  a  noble  clientele. 
Were  the  vague  alternatives  any  better  grounded  than 
the  definite  and  beautiful  hypothesis  of  Laplace? 
Obviously  there  was  no  logical  resting-place  for  one's 
confidence  short  of  some  definite  foundation  that  would 
stand  the  searching  tests  of  dynamics,  or  at  least  seem  to 
do  so.  It  was  idle  to  say  that  we  can  proceed  without 
basal  concepts;  if  they  are  not  consciously  adopted,  they 
unconsciously  insinuate  themselves  and  thus  take  on  their 
most  deceitful  forms.  The  unctuous  feeling  that  one  is 
dealing  "  only  in  solid  facts  "  is  too  often  merely  a  tenuous 
cover  for  subconscious  speculations  that  swarm  in  the 
turbid  substratum  of  thought.  It  is  easy  of  course  to  be 
content  with  the  protruding  elements  of  thought  and  to 
neglect  the  assumptions  on  which  they  unwittingly 
float;  it  is  easy  to  be  quite  sure  of  the  obtrusive  products 
and  quite  unconscious  of  the  assumptions  and  specula- 
tions which  may  be  their  only  buoy.  The  nearest 


74  THE  ORIGIN  OF  THE  EARTH 

approach  to  security  that  can  be  attained  lies  in  tracing 
all  tenets  back  as  far  as  possible,  with  critical  examina- 
tion of  their  grounds,  yielding  assent  to  them  only  in 
proportion  as  they  link  themselves  with  the  best  estab- 
lished principles  that  condition  natural  phenomena. 

INQUIRY  ALONG   OTHER   GASEOUS   LINES 

In  the  attempt  to  find  a  tenable  view  of  the  origin  of 
our  planetary  system — an  attempt  which  naturally 
followed  loss  of  faith  in  the  Laplacian  and  related  hy- 
potheses— no  success  was  had  along  gaseous  lines. 
The  tests  based  on  the  kinetic  theory  of  gases  and  on  the 
laws  of  dynamics  seemed  to  cut  a  deadly  swath  through 
all  assignable  outgrowths  of  gaseous  states  so  far  as  these 
have  had  to  do  with  our  oum  planetary  system.  I  beg  that 
this  distinction  between  our  planetary  system  and  other 
possible,  and  probably  actual,  planetary  systems  be 
kept  clearly  in  mind.  There  is  no  question  that  a 
certain  group  of  the  nebulae  are  gaseous,  and  there  is 
good  ground  to  believe  that  such  nebulae  develop  second- 
ary systems  -plane  tan',  planctoidal,  or  otherwise— 
along  consistent  gaseous  lines;  but  the  evidence  brought 
out  by  the  previous  inquiry  seemed  to  leave  no  ground 
to  believe  that  our  planetary  system  arose  in  this  way. 
All  efforts  in  gaseous  lines  appeared  thus  not  only  to  be 
futile  but  there  seemed  to  be  no  encouragement  for 
further  efforts  with  any  medium  over  which  laws  of  the 
collision-rebound  type  presided. 

INQUIRY   ALONG   METEORITIC   LINES 

To  this  last  category  belong  all  meteoritic  hypotheses 
of  the  quasi-gaseous  type,  that  is,  all  meteoritic  hy- 


FUTILE  EFFORTS  75 

potheses  in  which  the  deployment  of  the  meteoric 
swarm  is  supposed  to  be  maintained  by  collisions  and 
rebounds  of  the  constituent  meteorites.  Sir  George 
Darwin  has  shown,  in  a  masterly  mathematical  study, 
that  if  meteorites  are  assembled  so  as  to  collide  and 
rebound  in  a  miscellaneous  way  as  do  the  molecules  of 
gases,  and  if,  in  such  collisions,  essentially  perfect 
elasticity  is  brought  into  play  by  the  generation  of  gas 
at  the  points  of  impact  and  the  instant  expansion  of  this 
gas,  the  whole  assemblage  will  follow  the  laws  of  a 
gaseous  body;  the  meteorites,  at  least  up  to  sizes  com- 
parable to  the  cannon  balls  of  former  days,  may  be 
treated  as  gigantic  molecules.1  The  uncertain  point  in 
this  deduction  lies  in  the  doubt  whether  meteorites 
in  collision  would,  as  a  matter  of  fact,  develop  the  elastic 
recoil  essential  to  the  validity  of  the  conclusion.  If 
not,  the  collapse  of  the  assemblage  would  apparently 
be  more  rapid  than  that  of  a  true  gaseous  body  and  the 
evolution  of  heat  would  be  faster;  the  liability  to  pass 
into  a  true  gaseous  condition  would  thus  be  imminent. 
But,  whichever  alternative  obtained,  the  behavior 
of  a  quasi-gaseous  swarm  of  meteorites  would  follow  the 
same  general  course  as  the  evolution  of  a  gaseous  nebula. 
In  neither  of  these  meteoritic  alternatives  should  the 
swarm  normally  have  a  larger  ratio  of  centrifugal  momen- 
tum to  mass  than  does  a  gas — nor  should  the  momentum 
be  better  distributed.  Now  Moulton's  trenchant  studies 
have  shown  that  a  gas,  normally  distributed  according 
to  the  law  of  gases,  does  not  carry  enough  moment  of 
momentum,  nor  the  right  distribution  of  moment  of 
momentum,  to  develop  into  such  a  planetary  system  as 
ours.  At  first  sight,  the  quasi-gaseous  form  of  meteoritic 


76  THE  ORIGIN  OF  THE  EARTH 

hypothesis  has  its  attractive  features,  but  on  closer 
scrutiny  it  appears  that  it  is  not  more  promising  than 
the  true  gaseous  hypotheses,  if  indeed  it  is  not  in  some 
respects  less  promising,  even  if  we  ignore  all  grounds 
of  doubt  as  to  the  reality  of  such  a  nebular  constitution. 
There  are,  however,  other  meteoritic  hypotheses. 
The  most  strictly  meteoritic  of  them  all  is  that  old 
view  which  took  its  cue  from  the  observed  habit  of  the 
meteorites  that  nightly  illumine  our  present  skies. 
From  this  it  reasoned  backward  in  logical  consistency. 
It  perhaps  alone  is  meteoritic,  in  the  strictest  sense,  in 
that  it  deals  with  true  meteorites  actuated  by  the 
demonstrable  habits  of  meteorites.  The  reasoning 
runs  as  follows:  The  earth  now  gathers  in  meteorites 
daily  by  millions;  there  must  be  just  so  many  millions 
less  in  open  space  today  than  there  were  yesterday ;  there 
must  have  been  millions  more  at  each  earlier  interval 
than  in  each  later  one;  more  were  picked  up  daily  in 
early  times  than  now;  in  the  very  early  days,  the 
accretion  was  very  rapid  and  the  growth  fast.  This 
is  logical  thus  far;  but  the  hypothesis  halts  or  grows 
vague  just  when  it  should  press  on  sharply  to  the  initial 
point,  the  point  on  which  even-thing  hangs.  Up  to  its 
halt  the  working  basis  is  the  f>rc-cxistcnce  of  the  earth 
and  its  service  as  a  collecting-center.  The  hypothesis 
spends  its  force  upon  this  source  of  unquestioned 
growth  while  it  fails  to  point  out  the  origin  of  the 
mechanism  of  which  this  growth  is  an  incident.  When 
scrutinized  relative  to  the  essential  initial  condition, 
it  seems  specially  incompetent,  for  meteorites  are  seen 
to  be  plunging  through  space  with  various  velocities  in 
various  directions  and  in  a  very  sporadic  way,  except 


FUTILE  EFFORTS  77 

as  they  are  the  relics  of  dispersed  comets  which  are 
themselves  scarcely  less  erratic.  The  velocities  of  the 
meteorites  are  so  various  and  high  as  to  imply  a  dis- 
persive rather  than  a  segregative  tendency.  They 
offer  no  suggestion  as  to  how  a  planetary  nucleus  could 
spring  from  them.  Their  momentum  is  so  vastly 
superior  to  their  gravitative  power  that  the  conditions 
they  offer  appear  to  be  distinctly  inimical  to  segre- 
gation except  as  they  are  caught  by  some  masterful 


Even  if  this  fundamental  difficulty  could  be  avoided, 
it  does  not  appear  that  there  is  any  systematic  pre- 
ponderance of  infall  from  any  one  direction,  except  as 
local  showers  arise  from  dispersed  comets,  and  even  these 
are  as  heterogeneously  disposed  as  were  their  parent 
comets.  But  a  marked  preponderance  is  prerequisite 
to  the  disk-like  arrangement  of  the  planetary  revolu- 
tions, one  of  the  most  pronounced  characteristics  of  the 
system. 

At  best  then  this  line  of  search  merely  leads  back  to 
the  vital  questions:  What  gave  origin  to  the  planetary 
centers  of  collection?  What  made  the  planets  revolve 
nearly  in  the  same  plane  ?  Efforts  along  this  meteoritic 
line  —  the  true  meteoritic  line  —  seem  therefore  futile, 
if  the  search  is  for  the  origin  of  the  planetary  system. 
This  meteoritic  hypothesis  merely  lays  emphasis  on  a 
mode  of  growth  —  undue  emphasis,  it  would  appear, 
on  what  is  probably  a  merely  incidental  rather  than  an 
essential  mode  of  growth.  Meteoritic  growth  at  present 
is  so  extremely  small  as  to  be  practically  negligible,  as 
shown  by  Woodward  and  others.  There  is  little 
or  no  specific  support  for  any  presumption  that  such 


78  THE  ORIGIN  OF  THE  EARTH 

meteoritic  growth  ever  rose  in  geologic  time  to  appreci- 
able quantitative  value. 

The  naturalistic  mode  of  testing  this  hypothesis,  by  an 
appeal  to  the  vestiges  of  former  conditions  presented 
by  the  meteorites  themselves,  and  the  significant 
features  of  their  singular  structures,  is  of  the  same 
general  import.  Meteorites  have  rather  the  char- 
acteristics of  the  wreckage  of  some  earlier  organization 
than  of  the  parentage  of  our  planetary  system. 

In  a  third  class  of  views  grouped  as  meteoritic,  in  the 
loose  sense  of  that  term,  nebulae  are  interpreted  as 
assemblages  of  meteorites  pursuing  orbits  about  a 
center  of  gravity.  The  orbital  feature  of  the  hypothesis 
carries  the  case  over  into  quite  another  field  of  dynamics, 
orbital  dynamics,  and  a  prompt  growl  of  protest  from  the 
traditional  "lion  in  the  way''  is  naturally  provoked.  It 
was  currently  held  during  the  last  century  that  the 
whole  field  of  orbital  evolution  was  effectually  barred 
by  the  deduction  that  retrograde  rotations  would 
result  from  the  aggregation  of  bodies  in  orbital  revolu- 
tion, because  as  a  matter  of  fact  the  larger  number 
of  rotations  in  our  planetary  system  are  coincident 
with  the  revolutions.  So  long  as  this  "lion  in  the 
way''  of  cosmogonic  adventurers  was  held  to  be 
living  and  real,  it  was  of  course  idle  to  seek  an 
origin  of  our  planetary  system  by  an  evolution  from 
meteorites  in  orbital  revolution  around  a  common 
center. 

But,  neglecting  this  traditional  difficulty  for  the  time 
being,  certain  other  limitations  aiTecting  evolution 
under  orbital  dynamics  are  to  be  taken  into  serious 
consideration.  The  cooling  and  shrinking  of  celestial 


FUTILE  EFFORTS  79 

bodies  have  no  effect  on  their  orbital  motions,  and  hence 
cooling  and  shrinkage,  which  play  so  large  a  part  in 
familiar  cosmogonic  hypotheses,  have  no  vital  function 
in  evolution  under  orbital  conditions.  Under  such 
conditions  the  vital  issue  concerns  collecting  centers  and 
conjunctions  of  orbits.  If  small  bodies  pursuing  indi- 
vidual courses  cross  the  orbits  of  adequate  collecting- 
centers,  they  furnish  the  mechanism  of  growth.  Without 
adequate  collecting  centers  such  crossings  are  more 
likely  to  promote  fragmentation  and  dispersion  than 
aggregation. 

If  the  orbits  of  the  small  bodies  to  be  gathered  into 
planets  strike  in  all  directions  promiscuously — are 
quaquaversal  as  the  geologist  would  say — it  is  clear  that 
the  case  is  unpromising  for  the  evolution  of  planetary 
disk  such  as  the  actual  case  requires.  The  concentra- 
tion of  such  a  quaquaversal  system  tends  toward  a 
globular  aggregate  in  which  heterogeneous  collisions 
prevail.  More  or  less  concurrent  orbital  revolutions 
are  required  to  give  rise  to  a  concentric  harmonious 
organization  of  discoidal  form.  Concentration  in  a 
quaquaversal  case  really  trends  in  the  direction  of  a 
gaseous  body  and  in  most  cases  of  notable  mass,  and 
complexity,  any  close  concentration  of  the  assemblage 
would,  with  little  doubt,  result  in  a  passage  into  an 
actual  gaseous  aggregate. 

In  the  vital  matter  of  momentum,  the  tendency  in 
such  a  case  is  toward  a  low  value,  since  revolutions 
in  opposite  directions  more  or  less  offset  one  another 
in  aggregation  and  only  the  algebraic  sum  of  the  indi- 
vidual momenta  remains.  Considered  thus  from  the 
critical  point  of  view  of  momentum  values,  the  case  is 


8o  THE  ORIGIN  OF  THE  EARTH 

unpromising.  Apparently  the  only  line  of  escape  from 
this  untoward  trend  lies  in  postulating  a  distinct  pre- 
ponderance of  revolutionary  values  in  one  direction  over 


Fie.  i. — The  spiral  nebula  M  74  Piscium,  a  symmetrical  form, 
whose  two  arms  bear  a  notable  scries  of  knots  that  seem  admirably 
adapted  to  be  collecting  centers  for  the  adjacent  nebulous  matter. 
Photographed  at  the  Lick  Observatory. 

those  in  all  other  directions,  which,  in  reality,  is  the 
abandonment  of  the  case  and  the  substitution  of  a  new 
case,  that  of  orbital  revolutions  dominantly  of  the  same 
phase. 


FUTILE  EFFORTS  81 

This  substitute  offers  a  nearer  approach  to  working 
conditions.  It  seems  at  least  to  lie  in  the  right  direction, 
if  only  the  rotational  bar  is  not  prohibitive.  When, 
however,  constructive  effort  is  pursued  along  this  line, 
it  becomes  at  once  obligatory  to  point  out  or  to  postulate 
— with  reasons  therefor — the  necessary  collecting  centers 
in  proper  number  and  relations — four  powerful  centers 
to  gather  in  the  orbital  matter  to  form  the  four  great 
planets;  four  centers  of  medium  efficiency  to  collect 
matter  for  the  four  minor  planets;  a  multitude  of  small 
centers  to  grow  into  the  hundreds  of  planetoids,  and 
withal  several  small  groups  of  secondary  centers  revolv- 
ing around  the  planetary  centers  to  segregate  into 
satellites.  Matter  in  orbital  motion  does  not  aggregate 
spontaneously  in  the  simple  fashion  that  obtains  with 
static  matter.  The  required  nuclei  of  aggregation  do 
not  seem  to  be  natural  elements  in  a  simple  spheroidal 
or  discoidal  nebula  where  each  small  body  is  pursuing 
an  orbit  of  its  own.  Observational  evidences  of  nuclei, 
or  cogent  dynamical  reasons  for  their  origination,  do  not 
seem  to  be  at  hand. 

Such  centers  of  aggregation  are,  however,  marked 
features  of  spiral  nebulae,  whose  arms  are  singularly 
affected  by  knots  which,  in  the  nature  of  the  case,  may 
be  confidently  assumed  to  function  as  collecting  centers. 
These  spiral  nebulae,  however,  constitute  a  class  quite 
distinct  from  spheroidal  aggregates  and  claim  attention 
on  then:  own  grounds.  It  is  interesting  here  to  note, 
however,  that,  in  so  far  as  spheroidal  nebulae  are  con- 
structively modified  to  take  on  promising  qualities,  they 
approach  the  characters  possessed  in  a  more  eminent 
degree  by  spiral  nebulae  (see  Fig.  i). 


82  THE  ORIGIN  OF  THE  EARTH 

INQUIRY  ALONG  COLLISIONAL  LINES 

More  than  a  century  ago  the  naturalist  Buffon  ad- 
vanced the  theory  that  our  planetary  system  arose  from 
the  collision  of  a  great  comet  with  the  sun.  While  later 
knowledge  of  comets  has  rendered  this  view  quite 
untenable,  Buffon  gave  definite  initiation  to  the  col- 
lisional  genus  of  cosmogonic  hypotheses.  Collisional 
views  of  genesis  of  various  less  obviously  untenable 
types  have  been  entertained  since.  Without  doubt 
the  possibilities  of  collision  are  entitled  to  a  place  among 
cosmogonic  studies,  for  encounters  undoubtedly  occur 
and  almost  inevitably  they  must  be  followed  by  some 
form  of  reorganization  or  recollection  of  the  scattered 
matter,  though  this  does  not  necessarily,  nor  perhaps 
generally,  imply  a  reunion  into  a  single  body.  The 
question  in  hand,  however,  is  the  narrower  one:  Did 
any  form  of  collision  initiate  the  conditions  out  of  which 
our  planetary  system  arose?  The  verity  of  the  genus 
is  not  proof  of  the  species,  much  less  of  the  individual 
case.  Here,  as  before,  the  decisive  criteria  are  to  be 
sought  in  such  vestiges  of  its  earlier  stages  as  are  still 
borne  by  our  planetary  family. 

The  conditions  to  be  met  are  definitely  fixed;  the 
result  of  the  collision  must  yield  a  central  mass  of  the 
magnitude  of  our  sun ;  this  must  be  surrounded  at  once 
or  ultimately  by  eight  rather  large  masses  and  a  multi- 
tude of  small  masses,  all  in  subcircular  revolutions. 
These  smaller  masses  must  together  equal  about  ij-J-y  of 
the  total  mass.  This  small  factor  must  carry  98  per  cent 
of  the  moment  of  momentum  of  the  whole  system. 

Now  center-to-center  collisions,  or  anything  approach- 
ing such  collisions,  seem  to  be  excluded  by  these  con- 


FUTILE  EFFORTS  83 

ditions,  for  if  the  impinging  body  were  small,  it  would 
be  simply  swallowed  up  in  the  great  solar  mass;  if  it 
were  sufficient  in  mass  or  in  velocity  completely  to 
traverse  the  solar  body,  the  result  probably  would 


FIG.  2. — The  ring  nebula  in  the  constellation  Lyra.    Photographed  at 
the  Lick  Observatory. 

partake  of  the  nature  of  a  vortex  of  the  smoke-ring  type. 
The  ring  nebulae  may  possibly  fulfil  the  requirements 
of  such  a  case,  though  other  possible  interpretations 
of  these  singular  objects  may  be  entertained  (Fig.  2). 
Extreme  dissociation  no  doubt  would  follow  such  a 


84  THE  ORIGIN  OF  THE  EARTH 

piercing  stroke,  since  the  velocity  of  collision  would  be 
high  if  the  mass  of  an  average  star  were  involved.  The 
spectroscopic  natures  of  the  ring  nebulae  tally  with  this 
presumption. 

It  is  difficult  to  imagine  a  case  of  head-on  collision  that 
could  leave  its  wreckage  in  a  state  suitable  for  gathering 
into  a  system  like  our  own,  for  radial  dispersion  is  the 
normal  result.  The  only  case  of  promise  is  a  glancing 
collision;  that  at  first  seemed  to  be  quite  hopeful  and 
was  industriously  tried. 

In  cases  of  glancing  collision  certain  conditioning 
features  are  inevitable  and  need  to  be  taken  seriously 
into  account.  The  course  of  the  impinging  body  at  the 
time  of  impact  is  a  sharp  curve,  not  a  straight  line  as 
sometimes  pictured.  This  curvature  is  further  con- 
ditioned by  a  severe  tidal  strain  due  to  the  differential 
attraction  of  the  two  bodies  then  very  close  together,  and 
this  alone  involves  danger  of  disruption,  if  not  of  violent 
projection,  even  before  collision  takes  place.  If  the 
impinging  body  is  affected  by  high  internal  elastic  com- 
pression, expansion  enters  also  into  the  combination  of 
conditions,  since  gravity  is  neutralized  on  certain  lines 
and  supplemented  on  others  by  compression  and  this 
adds  to  the  disruptive  and  dispersive  tendencies.  Only 
in  an  exceptional  case,  if  at  all,  is  it  safe  to  assume  that 
an  impinging  body  at  the  instant  it  nears  collision  with  a 
massive  body  of  the  order  of  thesuncan  maintain  its  integ- 
rity under  the  disrupting  influences.  If  it  is  gaseous  at 
the  start,  it  must  yield  freely  to  the  dispersive  tendencies. 

The  velocities  at  which  collisions  would  normally  take 
place  are  forbiddingly  high,  and  excessive  dispersion 
becomes  almost  inevitable.  The  case  in  hand  requires, 


FUTILE  EFFORTS  85 

as  its  minimum,  the  mass  of  the  sun  plus  the  mass  of  the 
planets.  A  planetary  body  merely  falling  under  gravity 
from  some  point  outside  the  sun's  normal  sphere  of 
control  would  have  a  velocity  of  the  order  of  three 
hundred  and  eighty  miles  per  second  at  the  instant  of 
collision.  It  is  possible  to  escape  some  of  this  trouble- 
some velocity  by  assuming  that  the  solar  body  was  in  an 
expanded  condition.  A  glancing  impact  would  then 
take  place  at  a  greater  distance  from  the  center  of 
gravity  and  the  velocity  would  be  correspondingly 
lower.  It  is  scarcely  permissible,  however,  to  assume 
that  the  expansion  reached  the  orbit  of  the  innermost 
planet  about  to  be  formed,  for  that  would  prevent 
the  deployment  of  that  planet.  And  so  the  velocity  of 
collision  could  not  well  be  reduced  below  fifty  miles  per 
second  by  postulating  expansion.  Even  this  cannot  be 
done  without  incurring  some  incidental  difficulties,  for 
the  outer  border  of  so  expanded  a  sun  would  be  very 
attenuated  and  perhaps  formed  chiefly  of  the  lightest 
gases,  which  would  not  be  felicitous  material  for  forming 
the  earth.  Perhaps,  however,  this  might  be  assigned 
to  the  colliding  body. 

It  is  difficult  to  picture  the  effects  of  collisions  of 
velocities  ranging  from  fifty  to  three  hundred  and  eighty 
miles  per  second.  Extreme  dispersion  would  seem  to  be 
inevitable,  perhaps  even  atomic  dissociation.  The 
line  of  dispersion  should  radiate  from  the  point  of  impact, 
and  one  can  scarcely  imagine  the  formation  of  aggregates 
to  serve  as  centers  for  the  collection  of  planets  in  the 
dispersed  matter.  As  only  a  portion  of  one  or  both 
bodies  is  supposed  to  be  in  direct  collision,  the  rest 
might  limit  the  dispersion  in  its  direction  and  give  it 


86 


THE  ORIGIN  OF  THE  EARTH 


the  semi-radial  form  seen  in  several  cases  in  the  heavens, 
of  which  the  two  great  nebulae  of  Orion  are  the  most 


FIG.  3.— The  Great  Nebula  in  Orion  and  the  Fish-Mouth  Nebula. 
Photographed  at  the  Yerkes  Observatory. 

notable  examples  (Fig.  3).    These  may  possibly  have 
been  co-partners  in  a  mutual  collision. 


FUTILE  EFFORTS  87 

The  intensity  of  dispersion  and  its  divergent  radial 
nature  are  serious  difficulties  in  the  way  of  forming  a 
plausible  hypothesis  of  the  formation  of  a  planetary  sys- 
tem such  as  ours  as  the  sequel  of  a  glancing  collision. 
Before  serious  inspection,  the  case  of  a  small  meteoroidal 
nebula  driving  nearly  tangentially  into  the  very  attenu- 
ated border  of  a  large  solar  nebula  seemed  to  me  to 
present  a  hopeful  basis  for  such  a  hypothesis,  and  con- 
siderable constructive  effort  was  spent  in  the  endeavor  to 
find  consistent  working  conditions  that  might  eventuate 
in  our  planetary  system,  but  in  addition  to  the  infelici- 
ties of  dispersion  arising  from  high  velocities  of  collision, 
other  formidable  obstacles  arose. 

It  is  a  law  of  celestial  mechanics  that  bodies  thrown 
into  orbital  paths  by  encounters  must,  in  completing 
their  courses,  return  to  the  point  of  collision,  which  in 
this  case  would  be  the  edge  of  the  sun,  or  of  the  body 
that  was  to  form  the  sun.  Of  course  bodies  might 
be  driven  off  so  violently  as  to  fly  beyond  the  sphere  of 
control  of  the  solar  mass  and  be  irrecoverable,  and  this 
would  be  a  rather  imminent  contingency,  but  all  such 
dispersed  matter  as  remained  under  solar  control — and 
this  of  course  included  all  that  could  enter  into  the 
formation  of  planets — was  compelled  to  come  back  to  the 
point  of  collision  and  be  subject  to  renewed  collision,  and 
so  on  indefinitely.  Some  partial  escape  from  these 
fatal  conditions  might  arise  in  the  case  of  such  molecules 
or  other  highly  elastic  bodies  as  experienced  secondary 
collisions  in  the  course  of  their  flights  and,  by  reaction 
from  these,  established  new  orbits,  with  a  necessity  of 
returning  to  the  point  of  this  secondary  collision  where 
the  chance  of  a  new  encounter  might  be  lessened. 


88  THE  ORIGIN  OF  THE  EARTH 

There  might  also  be  some  escape  when  the  attraction 
of  the  impinging  body,  after  collision,  drew  the  flying 
matter  into  new  orbits,  if  the  impinging  body  remained 
in  a  sufficiently  aggregated  state  to  exert  any  appreciable 
centralized  attraction.  The  effectiveness  of  either  or 
of  both  of  these  diversions  working  together  is  very 
doubtful.  In  any  case  the  new  orbits  were  likely  to 
remain  very  eccentric  and  to  have  their  perihelion 
points  near  the  sun. 

There  are  ways  in  which  eccentric  orbits  may  be 
reduced  to  subcircularity,  but  the  extreme  eccentricity  of 
the  orbits  that  would  arise  from  collision,  and  the 
difficulty  of  finding  any  applicable  and  adequate  agency 
for  the  reduction  of  these  orbits  to  the  requisite  sub- 
circular  form  of  the  present  planetary  orbits,  and  for 
giving  them  the  spacing  of  the  existing  system,  seemed 
to  be  so  far  insuperable  that  constructive  effort  in  this 
line  was  abandoned.* 

This  disappointing  outcome,  however,  had  a  directive 
effect.  As  in  the  inquiry  on  meteoroidal  lines,  the 
results  suggested  the  general  direction  in  which  a  suc- 
cessful hypothesis  must  probably  lie.  Even  more 
directly  than  in  the  meteoroidal  case,  they  pointed 
to  spiral  nebulae  as  promising  forms.  Celestial  col- 
lisions were  indeed  one  of  the  sources  to  which  the  origin 
of  spiral  nebulae  was  then  referred.  While  such  a 
genesis  of  spiral  nebulae  could  scarcely  be  regarded  as 
supported  by  the  considerations  we  have  just  reviewed, 
some  related  source  might  perhaps  be  found  to  fit 
both  the  origin  of  the  spirals  and  the  genesis  of  our 
planetary  system.  The  supreme  weakness  of  referring 
spiral  nebulae  to  eccentric  collisions  lies  in  the  fact 


FUTILE  EFFORTS  89 

that  such  an  origin  implies  a  single  spiral  arm  or  set  of 
arms,  springing  from  the  side  of  the  nucleus  at  which  the 
collision  took  place,  whereas  spiral  nebulae  habitually 
show  two  arms  or  sets  of  arms  arising  from  diametrically 
opposite  sides  of  the  central  mass.  Some  other  source 
for  spiral  nebulae,  and  for  our  planetary  system  alike, 
seemed  to  be  indicated  by  the  study  of  collisional  effects. 
But  the  "lion"  was  in  the  way  here.  The  deploy- 
ment of  spiral  nebulae  makes  it  extremely  improbable 
that  their  arms,  their  knots,  and  their  scattered  matter 
have  any  material  support  such  as  the  resting  of  the 
outer  parts  on  the  inner  parts,  as  in  the  case  of  gaseous 
bodies.  Each  part  must  obviously  move  in  an  inde- 
pendent path  and  be  supported  by  its  own  moving 
force.  Thus  these  bodies,  above  perhaps  any  other 
nebulous  form  in  the  heavens,  lay  under  the  rotational 
ban.  All  such  bodies,  it  was  said,  should  have  retro- 
grade rotations,  whereas  most  of  the  planets  have  forward 
rotations.  If  this  "lion  in  the  way"  was  a  real  lion,  it 
was  idle  to  waste  time  on  spiral  nebulae,  unless  it  could 
be  shown  that  the  lion  was  chained  to  some  special  case 
or  condition  which  the  creative  process  had  in  some  way 
avoided  in  forming  our  system. 

REFERENCES 

1.  Sir  George  Darwin,  "On  the  Mechanical  Conditions  of  a  Swarm 
of  Meteorites,  and  on  Theories  of  Cosmogony,"  Phil.  Trans.  Roy.  Soc. 
London  (1888),  pp.  1-29;  Nature,  XXXI  (1884-85),  25. 

2.  "Report  of  T.  C.  Chamberlin,"  Carnegie  Institution  of  Washington, 
Year  Book  No.  2  (1903),  pp.  261-70;  ibid.,  Year  Book  No.  3  (1904), 
pp.  195-208. 


CHAPTER  V 
THE  FORBIDDEN  FIELD 

As  already  noted  once  and  again,  there  seemed  to  be  a 
lion  in  the  way  of  entering  the  field  of  orbital  organiza- 
tion in  search  of  the  origin  of  our  planets — an  adverse 
argument,  a  hostile  demonstration,  so  clear  and  cogent 
that  it  stood  as  a  prohibitive  ban.  It  ran  in  this  wise: 
In  every  bcxly  rotating  as  a  spheroid,  or  as  a  disk,  or  as  a 
coherent  ring,  the  outer  part  moves  faster  than  the  inner 
part,  and  hence  if  a  ring,  or  any  symmetrical  section, 
separates  and  condenses,  the  faster  outer  parts  swing 
forward  around  the  slower  inner  parts  and  the  rotation 
is  forward  in  all  normal  cases.  The  argument  is  made 
all  the  more  conclusive  if  it  is  observed  that,  even  before 
separation  and  condensation,  the  outer  part  was  swing- 
ing round  the  inner  part  once  with  every  rotation  of  the 
whole.  The  part  in  question  thus  already  had  a  for- 
ward rotation,  and  this  rotation  would  of  course  be  accel- 
erated by  any  contraction  that  might  follow  (Fig.  4). 
On  the  other  hand,  if  the  spheroid,  disk,  or  ring  were 
formed  of  discrete  particles,  each  revolving  in  its  own 
independent  orbit,  the  inner  particles,  as  a  necessity  of 
the  orbital  state,  must  move  faster  than  the  outer  ones, 
and  so,  when  any  symmetrical  section  of  these  inde- 
pendent bodies  collects  into  a  single  mass,  the  higher 
velocity  of  the  inner  bodies  imparts  a  retrograde  rota- 
tion to  the  conjoined  mass  (Fig.  5).  The  reasoning 
seems  irreproachable. 

90 


THE  FORBIDDEN  FIELD 


But  is  this  second  case  really  representative  ?  Does 
it  even  belong  to  the  type  of  organization  we  wish 
to  put  to  trial  as  a  possible  source  of  origin  of  our 
planets  ? 

It  is  clear  that  the  case  was  fashioned  from  the  picture 
of  Laplacian  rings,  Saturnian  rings,  and  similar  sym- 
metrical forms  in  which  a  very  regular  concentric  arrange- 
ment of  circular  orbits  obtains.  In  these  cases  it 
was  tacitly  assumed  that,  in 
collecting,  the  orbits  would 
remain  circular  and  the  con- 
centric arrangement  continue 
to  prevail.  Without  con- 
sciously specifying  it,  the 
collecting  process  appears  to 
have  been  assumed  to  arise 
from  a  symmetrical  enlarge- 
ment of  the  inner  orbits,  or 
a  symmetrical  shrinkage  of 
the  outer  orbits,  or  both 
together,  with  no  essential 
alteration  of  their  concentric 
relations  or  their  circular 
forms.  And  yet  it  is  clear 
that  if  the  orbits  were  so  slightly  disturbed  or  dis- 
torted that  a  faster-moving  inner  body  should  swing 
out  only  so  far  as  to  strike  a  neighboring  body  on  its 
outer  half  rather  than  its  inner  half,  the  two  bodies 
would  rotate  forward.  This  illustration,  to  be  sure, 
involves  a  special  assumption  that  is  perhaps  not  normal 
to  the  case,  but  it  serves  to  show  how  slight  a  variation 
of  conditions  reverses  the  results. 


Fir..  4. — RR  represents  a 
ring  of  gas  moving  as  a  unit 
and  hence  the  outer  portion 
the  faster.  If  converted  into 
a  spheroid,  K,  centrally  loca- 
ted, the  rotation  is  forward,  as 
shown  by  the  arrow. 


THE  ORIGIN  OF  THE  EARTH 


Now  in  a  spiral  nebula  there  is  no  reason  to  suppose 
that  the  knots,  or  the  particles  of  the  haze,  revolve  about 
the  center  of  gravity  of  the  nebula  in  orbits  that  are 
either  strictly  circular  or  closely  concentric  with  one 
another.  On  the  contrary,  there  is  reason  to  suppose 
that  these  orbits  are  rather  notably  elliptical  and 
rather  diversely  related  to  one  another,  so  that  they  cross 

in  various  ways  and  at 
different  angles,  though 
in  a  general  way,  f airly- 
concordant .  Something 
of  this  sort  would  un- 
doubtcdlv  be  true  of 


FIG.  5. — PP  represents  a  belt  of 
planctcsimals  revolving  concentrically 
about  the  center,  .V.  If  these  collect 
about  the  central  point  of  the  belt 
into  a  spheroid,  K,  by  the  enlargement 
of  the  inner  orbits  or  the  reduction  of 
the  outer  ones,  the  concentric  arrange- 
ment remaining,  the  rotation  will  be 
retrograde,  as  shown  by  the  arrow. 


orbits  arising  from  col- 
lisions and  probably 
also  of  mctcoroidal  or- 
bits. Observation  and 
theoretical  inference 
alike  imply  that  circular 
orbits  are  the  exception 
in  the  heavens  rather 
than  the  rule.  Even  in 
a  sub-circular  system 
like  our  own,  the  ellip- 


ticities  of  the  orbits  are 
far  too  great  to  make  it  safe  to  predict  the  precise  way  in 
which  one  planet  would  strike  another,  if  their  orbits 
were  so  shifted  as  to  make  a  collision  possible.  Before 
the  results  of  a  conjunction  of  revolving  bodies  can  be 
treated  safely,  it  is  necessary  to  consider  the  specific 
modes  in  which  conjunctions  may  occur  and  the  veloci- 
ties that  obtain  at  the  instant  of  collision. 


THE  FORBIDDEN  FIELD  93 

In  the  first  place,  the  movement  of  a  body  in  an 
elliptical  orbit,  instead  of  being  uniform — as  is  the  case 
of  a  body  in  a  perfectly  circular  orbit — varies  from  a 
maximum  speed  when  nearest  the  controlling  body,  to 
a  minimum  speed  when  farthest  from  it.  In  the  second 
place,  conjunction  in  elliptical  orbits  of  different  types 
can  take  place  at  certain  points  only.  A  planetary  body 
moving  in  an  outer  elliptical  orbit  can  come  into  col- 
lision with  a  body  in  an  inner  elliptical  orbit  only  when 
some  part  of  the  outer  swing  of  the  inner  orbit  (the 
aphelion  portion)  coincides  with  some  part  of  the  inner 
swing  of  the  outer  orbit  (the  perihelion  portion).  The 
whole  case  of  rotatory  effects  hangs  on  the  relative  mo- 
tions of  the  two  bodies  in  these  portions  of  their  orbits 
irrespective  of  their  mean  velocities  in  their  whole  orbits. 
The  simplest  case  is  that  in  which  the  aphelion  point  of 
of  the  inner  orbit  coincides  with  the  perihelion  point  of 
the  outer  orbit.  This  point  is  then  the  only  one  at  which 
the  bodies  in  the  two  orbits  can  come  together.  Two  in- 
stances of  this  type  are  illustrated  in  Fig.  6.  The  relative 
velocities  in  such  cases  are  of  course  mathematically  de- 
terminable,  but,  without  computation,  it  is  easy  to  see  the 
essential  fact  by  simple  inspection.  Starting  at  either 
point  of  contact  it  may  be  seen  that  the  inner  body 
lacks  sufficient  velocity  to  maintain  its  distance  from  the 
controlling  center,  5,  for  it  falls  back  gradually  toward 
this  center  as  it  proceeds  until  by  so  doing  it  acquires 
velocity  enough  to  carry  it  back  and  out  to  the  point 
of  contact.  On  the  other  hand,  the  body  in  the  outer 
orbit  at  the  point  of  contact  has  more  than  enough 
velocity  to  maintain  its  distance  from  the  controlling 
center,  for  it  gradually  increases  its  distance  until  by  so 


94  THE  ORIGIN  OF  THE  EARTH 

T 


Fir..  6. — Diagram  illustrating  the  condition  under  which  collisions 
may  take  place  in  elliptical  orbits  of  the  planetary  type.  S  represents 
the  solar  mass  at  the  center  of  the  system,  I',  the  planetary  nucleus,  B  its 
orbit,  p  a  planetesimal  in  the  orbit  .1 .  smaller  than  B,  and  /'  a  planctcsi- 
mal  in  orbit  C\  larger  than  B.  The  case  has  been  so  chosen  as  to  repre- 
sent at  once  the  smallest  and  the  largest  orbits  of  typical  eccentricity  that 
can  come  into  contact  with  the  orbit  of  the  planetary  nucleus.  The  mini- 
mum extreme  is  found  when  the  aphelion  point  of  the  small  ellipse  A  coin- 
cides with  the  |>erihelion  jx)int  of  the  orbit  of  the  planetary  nucleus  B. 
In  no  other  |x>sition  can  the  orbit  .-I  touch  the  orbit  B.  The  maximum 
extreme  is  found  where  the  aphelion  jx>int  of  B  coincides  with  the  peri- 
helion point  of  C.  In  no  other  jxjsition  can  these  orbits  touch.  Between 
these  limiting  phases,  represented  by  the  orbits  .-1 ,  and  C,  there  are  an 
indefinite  number  of  possible  planetesimal  orbits  that  might  cut  the 
orbit  B.  but  in  all  cases,  except  where  the  orbits  were  like  B,  conjunction 
could  arise  only  when  a  more  or  less  aphelion  portion  of  an  inner  orbit 
touched  or  crossed  a  more  or  less  aphelion  portion  of  B.  If  the  orbits 
were  equal,  the  velocities  at  the  crossings  would  be  equal  and  the  rotating 
effects  would  be  nil,  or  neutralized,  and  if  they  were  nearly  equal,  the 
difference  would  be  slight,  so  that  the  effective  cases  are  those  of  the 
extreme  classes  represented.  Further  explanation  is  given  in  the  text. 


THE  FORBIDDEN  FIELD  95 

doing  its  velocity  is  sufficiently  reduced  to  permit  it  to 
swing  back  and  in  to  the  point  of  contact.  It  appears 
therefore  that  at  the  point  of  contact  the  body  in  the 
larger  orbit  is  moving  faster  than  the  body  in  the  smaller 
orbit,  a  precise  reversal  of  the  traditional  deduction  that 
served  as  a  prohibitive  ban. 

This,  however,  does  not  cover  the  whole  case.  A 
simple  reversal  of  the  traditional  dictum  falls  short  of 
the  essential  truth,  for  elliptical  orbits  may  come 
together  in  a  multitude  of  ways,  and  from  these,  con- 
trary effects  may  arise,  though  the  mean  effects  are 
of  the  same  .general  phase  as  in  the  special  case  chosen 
for  illustration.  For  example,  let  the  outer  swing  of  a 
smaller  elliptical  orbit  cut  across  the  inner  swing  of  a 
larger  elliptical  orbit.  The  effects  of  an  encounter  will 
then  depend  on  the  precise  point  at  which  the  collisional 
stroke  takes  place,  even  though  the  body  in  the  larger 
orbit  is  moving  faster;  for  if  this  faster  body  in  the  outer 
orbit  overtakes  the  slower  body  in  the  inner  orbit  as  the 
latter  is  approaching  the  crossing,  the  inner  side  of 
the  swifter  body  will  strike  the  outer  side  of  the  slower 
body  and  the  joint  rotational  effect  will  be  forward; 
but  if  the  slower  body  in  the  inner  orbit  has  already 
passed  the  crossing,  the  outer  side  of  the  swifter  body 
will  strike  the  inner  side  of  the  slower  body  and  the  joint 
rotation  will  be  retrograde.  Between  these  two  cases 
there  is  an  ideal  center-to-center  collision  with  no  rota- 
tory effect.  When  a  multitude  of  cases  are  involved,  as 
in  the  growth  of  a  planet  from  many  small  bodies,  all 
possible  phases  are  likely  to  be  realized  and  the  rotational 
result  will  be  merely  the  algebraic  sum  of  the  diverse 
effects.  What  the  balance  of  opposing  tendencies  will 


96  THE  ORIGIN  OF  THE  EARTH 

be  can  be  foreseen  only  from  the  probabilities  of  the 
case;  these  may  not  be  decisive  in  particular  cases,  but 
will  be, trustworthy  for  the  majority  of  cases. 

If  the  little  bodies  to  be  gathered  in  to  form  the 
planet  are  very  numerous  and  their  irregularities  of 
distribution  and  of  movement  arc  such  as  to  give  much 
the  same  effect  as  uniformity  in  the  net  result,  the 
spaces  within  which  the  two  classes  of  collisions  are  liable 
to  take  place  may  be  taken  to  represent  fairly  the 
probabilities  of  the  case.  These  spaces  for  that  belt 
in  which  the  opposing  effects  are  most  pronounced  and 
important,  and  essentially  decisive,  are  shown  in  Fig.  7. 

It  will  be  observed  that  the  inner  section  in  the  cylin- 
drical track  of  the  planet  wherein  collisions  favor  forward 
rotation  is  notably  greater  than  the  outer  section  wherein 
collisions  favor  retrograde  rotation.  If  similar  belts, 
within  the  two  chosen,  were  inspected,  until  the  whole 
of  the  planets'  track  were  covered,  the  results  would  be 
of  the  same  nature.  The  differences  in  the  opposing 
effects  would  be  found  to  decline  as  the  belts  approach 
one  another  and  the  rotational  effects  to  trend  toward 
zero.  Of  course  the  distribution  of  the  small  indepen- 
dent bodies  may  not  be  uniform,  even  in  the  aggregate, 
and  the  effects  of  their  inequalities  may  offset,  in  greater 
or  less  degree,  the  normal  advantages  in  favor  of  forward 
rotation.  So  also,  their  distribution  may  be  such  that 
the  net  impact  values  on  one  side  or  the  other  of  the 
orbital  plane  of  the  planet  may  exceed  those  centered  in 
that  plane,  and  a  more  or  less  oblique  rotation  may 
result;  indeed  this  is  almost  inevitable,  and  it  may  rise 
to  notable  consequence.  In  harmony  with  this,  nearly 
all  the  rotations  of  planets  are  oblique. 


THE  FORBIDDEN  FIELD  97 

These  deductions  are  made  on  the  assumption  that 
the  planet  is  not  already  rotating.  But  if  rotation  is 
already  established,  the  effects  will  be  modified  in  a 
very  interesting  way.  If,  for  example,  the  planet  already 


FIG.  7. — In  this  diagram,  S  represents  the  sun;  £,  a  representative 
planet  moving  toward  the  perihelion  of  its  orbit  and  about  to  encounter 
small  discrete  bodies,  ppp  (planetesimals),  in  the  aphelion  portion  of  their 
elliptical  orbits  which  are  smaller  than  the  orbit  of  E,  and  are  hence 
moving  slower  than  E.  E  is  to  be  imagined  to  be  spherical  and  its  track 
to  be  cylindrical.  £'  represents  another  position  of  the  same  planet 
moving  toward  the  aphelion  point  of  its  orbit  and  about  to  be  overtaken 
by  small  discrete  bodies  (p'p'p')  in  the  perihelion  parts  of  their  elliptical 
orbits  which  are  larger  than  that  of  E'  and  are  hence  moving  faster  than 
E'.  For  simplicity,  only  belts  of  the  breadth  of  E  and  E'  are  represented. 
To  make  a  complete  inspection,  it  is  only  necessary  to  draw  similar  belts 
between  the  two  chosen  until  the  whole  orbit  of  E-E'  is  covered.  On  the 
left-hand  side  of  the  figure,  the  shaded  area  represents  the  only  "portions 
of  the  paths  of  E  and  of  the  little  bodies  (ppp)  that  are  common  and 


98  THE  ORIGIN  OF  THE  EARTH 

has  a  forward  rotation,  it  will  be  seen,  on  inspecting 
the  left-hand  section  of  the  figure  again,  that  the  rota- 
tory motion  of  the  outer  part  of  the  planet  will  increase 
the  impact  values  on  that  side — which  favors  retrograde 
rotation — while  the  backward  motion  of  the  inner 
limb  of  the  planet  will  reduce  the  value  of  the  impacts 
on  that  side  which  favor  forward  rotation.  These  two 
cooperating  influences  thus  tend  to  counteract  the 
normal  effect  which  favors  forward  rotation.  It  is 


where  alone  collisions  can  take  place.  Since  /.  is  here  moving  faster 
than  />/>/>,  it  is  obvious  that  encounters  on  its  inner  half  favor  forward 
rotation,  while  encounters  on  its  outer  half  favor  retrograde  rotation. 
K  represents  retrograde  effect,  ami  /•*,  forward  effect. 

Inspection  shows  that  the  inner  set  lion  of  I.  within  which  collisions 
favoring  forward  rotation  can  take  place  is  notably  greater  than  the 
outer  section  within  which  collisions  favoring  retrograde  rotation  can 
take  place,  and  hence,  if  there  is  an  equable  distribution  of  the  small 
bodies,  K  is  likely  to  acquire  a  forward  rotation. 

On  the  right-hand  side,  the  small  discrete  bodies,  P'p'p't  move 
faster  than  /  '  and  in  overtaking  /.'  on  its  outer  side  tend  to  give  it  forward 
rotation,  while  if  they  strike  on  the  inside,  they  tend  to  impart  retro- 
grade rotation.  The  preponderance  of  sjxicc  here  forces  forward 
rotation  as  before.  Inspection  shows  that  the  same  would  be  true  of  the 
additional  belts  required  to  cover  the  whole  path  of  E,  E',  but  the 
difference  of  effect  would  be  less  in  these  interior  belts.  The  belts  chosen 
arc  those  in  which  the  difference  of  effect  would  be  greatest. 

These  conclusions  arc  drawn  on  the  assumption  that  E  had  no  rota- 
tion at  the  start. 

If  E  already  had  forward  rotation,  insj>cction  of  the  figure  shows  that 
the  rotation  would  tend  to  increase  the  force  of  the  impacts  in  the  outer 
section  on  the  left  of  the  figure  favoring  retrograde  rotation,  and  to 
diminish  those  favoring  forward  rotation  and  would  hence  be,  to  this 
extent,  unfavorable  to  increase  of  forward  rotation,  as  explained  in  the 
main  text.  If  E  already  had  a  retrograde  rotation,  inspection  shows  that 
the  force  of  the  impacts  favoring  forward  rotation  would  be  increased 
and  that  of  those  favoring  retrograde  rotation  reduced.  The  accessions 
would  then  tend  to  arrest  the  retrograde  rotation  and  ultimately  to 
reverse  it. 


THE  FORBIDDEN  FIELD  99 

easily  seen  that  if  the  previous  rotation  already  had  a 
certain  speed,  this  counteracting  effect  would  be  suffi- 
cient to  neutralize  any  assigned  normal  effect  and  there 
would  then  be  no  acceleration  of  the  previous  rotation. 
So,  too,  the  inherited  rate  of  rotation  might  be  such 
that  this  counteracting  effect  would  exceed  the  normal 
effect  and  tend  to  retard  the  rotation.  The  argument 
holds  equally  well  when  applied  to  the  conditions  repre- 
sented in  the  right-hand  section  of  the  diagram  where 
the  relations  of  the  planet  and  small  independent  bodies 
are  reversed. 

From  these  considerations  there  springs  the  very 
important  conclusion  that  there  is  an  equilibrium  value 
for  rotation  in  cases  of  this  kind.  If,  for  any  reason,  the 
planet,  while  undergoing  accretion,  acquires  a  rotational 
speed  above  this  value,  the  counteracting  effect  of  the 
accessions  will  tend  to  depress  the  rate  of  rotation  until 
the  equilibrium  rate  is  reached.  If  the  rotation  falls 
below  the  equilibrium  rate,  the  effect  of  the  accessions 
is  to  raise  it  to  the  equilibrium  value.  If  the  distri- 
bution, or  the  forms,  or  the  proportions  of  the  little 
infalling  bodies  are  changed,  the  equilibrium  rate  of 
rotation  is  likely  to  change  also,  and  the  net  effects  of 
further  accessions  will  tend  to  change  the  rotation  that 
prevailed  before  the  change  to  the  new  equilibrium  rate. 
There  is  thus  an  automatic  regulative  system  by  which 
the  rate  of  rotation  is  made  to  oscillate  about  an  equi- 
librium value. 

It  appears  then  that  planetary  rotations  arising 
from  the  accretion  of  multitudes  of  small  discrete  bodies 
moving  in  elliptical  orbits  are  more  likely  to  be  forward 
than  backward,  that  they  are  likely  to  be  more  or  less 


ioo  THE  ORIGIN  OF  THE  EARTH 

oblique,  and  may  even  be,  in  exceptional  cases,  so  highly 
oblique  as  to  be  in  effect  retrograde. 

It  appears  further  that  the  net  rotational  result  of 
many  accessions  is  merely  the  equated  value  of  their 
opposing  effects,  and  that  the  rotation  is  likely  to  oscil- 
late about  an  equilibrium  value.  This  value  is  very 
far  from  the  simple  sum  of  the  impact  values  of  all  the 
little  bodies.  Extremely  high  rotations— such,  for 
example,  as  would  lead  to  centrifugal  separation — seem 
unlikely  to  arise  under  these  conditions;  more  likely 
varying  values  of  moderate  rates  only,  affected  by  more 
or  less  obliquity,  would  result.  An  orbital  state  of 
nebular  matter  is,  therefore,  not  only  not  a  condition 
prohibitive  of  forward  rotations,  but  is  a  condition  dis- 
tinctly tributary  to  it.  It  seems  peculiarly  suited  to 
give  just  such  rotations  as  our  planetary  family  actually 
presents,  if  indeed  it  does  not  furnish  the  sole  condition 
under  which  such  a  singular  group  of  rotations  could 
naturally  arise. 


CHAPTER  VI 

DYNAMIC  ENCOUNTER  BY  CLOSE  APPROACH 
CELESTIAL   KINSHIPS 

The  inquiry  which,  at  the  outset,  had  led  to  destruc- 
tive criticism  and  later  to  futile  constructive  efforts  on 
old  lines,  now  turned  into  a  path  of  its  own.  The 
field  of  promising  endeavor  had  been  greatly  narrowed. 
The  previous  inquiry  had  given  hints  of  dynamic  kin- 
ships in  the  celestial  kingdom.  These,  emerging  later 
into  clear  light,  broadly  defined  the  issues  and  sharp- 
ened the  criteria.  The  dynamic  features  of  the 
solar  system  had  betrayed  two  distinct  genetic  strains, 
one  clearly  featured  in  the  central  body,  where  great 
mass,  low  momentum,  and  an  oblique  attitude  were 
generic  characteristics;  the  other,  equally  clearly 
featured  in  the  brood  of  attendants,  where  high  momen- 
tumj  low  mass,  and  an  appressed  form  were  generic 
characteristics.  While  without  doubt  the  planetary 
brood  were  the  offspring  of  the  central  body,  decentral- 
ized factors  of  the  sun,  there  were  unmistakable  signs  of 
another  parent.  The  planetary  system  must  clearly  have 
had  a  bi-parental  origin;  it  must  have  been  dioecious, 
as  a  botanist  would  say.  If  so,  all  mono-parental  or 
monoecious  modes  of  generation  must  be  regarded  as 
excluded.  No  form  of  self -segregation  from  primitive 
chaos  or  quasi-chaos,  no  form  of  self-partition  of  gase- 
ous, quasi-gaseous,  meteoritic,  or  sporadic  aggregates, 
no  form  of  self-generated  centrifugal  separation  of  a 

101 


102.  THE  ORIGIN  OF  THE  EARTH 

common  mass,  could  supply  the  two  dynamic  strains  so 
distinctly  portrayed  in  the  genetic  features  of  the  solar 
family.  Each  of  the  monoecious  modes  might  perhaps 
be  the  fissiperous  or  parthenogenic  parent  of  appropriate 
celestial  families  born  under  suitable  conditions,  at 
various  times  and  in  various  places  in  the  celestial 
kingdom,  but  not  the  parent  of  our  planetary  family. 

Partition  by  collision,  on  the  other  hand,  is  a  bi- 
parental  process  and  its  offspring  should  betray  their 
double  parentage  and  bear  bi-parental  characteristics. 
Beyond  question  collision  has  stood  in  a  parental 
relation  to  new  celestial  evolutions,  but  of  a  very  radical 
decentralized  type.  The  intensely  dispersive,  dissocia- 
tive, and  decentralizing  nature  of  collisions  seems  to  be 
ill-fitted  for  the  genesis  of  such  a  planetary  system  as 
ours;  collision  apparently  has  had  a  much  more  radical 
disintegrating  function  to  serve  in  celestial  economy. 
Its  very  violent  action  is  thought  to  have  given  rise  to  a 
radically  dissociative  species  of  the  dioecious  genus; 
our  planetary  system  must  apparently  be  the  offspring  of 
a  kindred,  but  milder,  less  decentralizing,  species  of  the 
same  genus. 

DYNAMIC  ENCOUNTER   WITHOUT  COLLISION 

A  hint  of  what  we  now  believe  to  be  the  true  line  of 
descent  was  caught  from  a  mathematical  study  of 
satellites  made  by  Roche  long  ago.1  By  a  beautiful 
deductive  investigation,  Roche  showed  that  if  a  satellite 
were  made  to  approach  its  primary  on  an  inrunning 
spiral,  it  would  not  preserve  its  integrity  until  it  came 
into  contact  with  the  surface  of  the  primary  but,  at  a 
distance  of  2 . 44  times  the  radius  of  the  latter,  the  satel- 


DYNAMIC  ENCOUNTER  BY  CLOSE  APPROACH      103 

lite  would  be  torn  asunder  by  the  differential  attraction 
of  the  primary,  provided  both  primary  and  satellite 
were  of  the  same  homogeneous  constitution,  and  pro- 
vided cohesion  and  other  modifying  conditions  were 
neglected.  The  special  case  has  little  obvious  bearing  on 
the  genesis  of  planets,  but  it  brought  into  a  striking 
concrete  form  a  principle  of  action  which,  when  general- 
ized and  modified,  seemed  to  shed  a  suggestive  light  on 
planetary  origin. 

In  large  bodies  cohesion  is  of  little  moment  relatively, 
when  matched  against  gravitation.  In  bodies  that  are 
gaseous,  cohesion  is  replaced  by  internal  repellency. 
Even  in  solid  bodies  of  the  planetary  order,  the  state 
of  internal  compression  probably  calls  into  play  degrees 
of  elastic  resiliency  that  more  than  match  cohesion. 
If  gravitation  were  neutralized  by  counter-attraction, 
our  planet  would  certainly  expand  vigorously  in  spite  of 
cohesion.  In  bodies  of  high  internal  temperature,  the 
elastic  repellency  rises  to  a  potential  source  of  powerful 
expansion.  In  the  sun,  there  is  a  persistent  eruptive 
tendency  of  great  power.  At  short  intervals,  great 
bolts  of  sun-substance  are  shot  forth  at  high  velocities 
(see  Figs.  8,  9,  10  and  n).  This  takes  place  without 
any  obvious  outside  stimulus,  or,  if  there  be  such  stimu- 
lus, it  is  not  declared.  Beyond  question  if  suitable 
strong  stimulus  from  without  were  brought  to  bear  on 
the  sun,  such  as  the  differential  attraction  of  a  passing 
star,  it  would  respond  with  eruptions  of  much  greater 
intensity  and  mass. 

It  thus  appears  that  from  so  simple  a  cause  as  the 
differential  gravity  called  into  action  by  the  close 
approach  of  one  massive  body  to  another,  there  may  arise 


104  THE  ORIGIN  OF  THE  EARTH 

a  graded  series  of  eruptions  ranging  from  fractional 
ejections  to  profound  disruption  and  dispersion,  accord- 
ing to  the  closeness  of  approach,  the  relative  masses  of  the 
bodies,  and  their  internal  state.  The  ejected  parts 
will  pursue  such  courses  as  may  be  imposed  on  them  by 
the  new  forces  of  attraction  brought  into  play  by  the 


FIG.  8. — Solar  prominences  illustrating  the  eruptive  state  of  the 
sun.  Photograph  taken  during  eclipse  May  28,  1900,  Yerkes  Observa- 
tory. 

changing  relations  of  the  two  bodies,  both  of  which 
are  necessarily  in  swift  curving  motion,  while  one  or 
both  are  losing  mass  by  disruptive  action. 

ASSIGNED  ORIGIN  OF   SPIRAL  NEBULAE 

To  follow  into  concrete  details  a  typical  celestial 
incident  of  this  kind,  let  it  be  assumed  that  the  general 
order  of  things  in  the  heavens,  at  the  time  our  planets 
were  born,  was  not  radically  different  from  what  it  is 
today.  Let  the  critical  event  be  nothing  more  unusual 
than  the  approach  of  one  star  to  another,  an  inevitable 
event,  since  stars  move  in  a  multitude  of  directions  and 
at  varying  speeds.  The  degree  of  closeness  of  approach 
may  obviously  range  from  actual  contacts  to  the  utmost 
distance  at  which  gravitative  stimulus  will  be  effective 


DYNAMIC  ENCOUNTER  BY  CLOSE  APPROACH      105 

in  promoting  great  eruptions.  Center- to-center  collision 
is  of  course  the  last  term  in  closeness  of  approach,  but 
that  belongs  to  another  genus.  A  merely  glancing 
collision  is  the  next  door  neighbor  to  the  closest  approach 
without  collision ;  between  these  two  lies  the  generic  line 
of  division.  That  collisions  occur  seems  to  be  implied 
by  the  flashing  forth  of  new  stars,  an  event  not  very 
infrequent.  According  to  the  law  of  probabilities,  there 
should  be  a  very  much  larger  number  of  approaches 
that  escape  collision — and  yet  are  relatively  near — thari 
of  collisions.  Inspection  of  the  conditions  of  the  case 
seems  to  show  that  a  very  close  approach  is  not  neces- 
sary to  call  forth  notable  eruptive  response  when  at 
least  one  of  the  bodies  is  already  highly  eruptive,  as  in 
the  case  of  our  sun.  This  being  true,  statistical  treat- 
ment makes  the  number  of  effective  approaches  a  very 
high  multiple  of  the  probable  number  of  collisions. 
Even  if  effective  results  were  confined  to  the  Roche 
limit — which  seems  to  be  far  from  the  case — there  should 
be  six  or  eight  effective  approaches  to  every  collision. 
In  such  close  approach  as  this,  however,  complete 
disruption  of  one  or  both  the  bodies  would  apparently 
take  place,  and  that  is  far  too  violent  to  fit  the  case  in 
hand.  While  it  is  possible  that  quite  a  small  star, 
or  other  small  body,  closely  approaching  the  sun  might 
develop  a  nebula  fitted  to  form  our  planetary  system, 
only  a  much  more  distant  approach  of  an  average  star 
would  be  suited  to  call  forth  such  relatively  small 
ejections  as  those  involved  in  the  genesis  of  our  planets. 
A  close  approach  involves  a  very  substantial  en- 
counter, though  it  is  a  purely  dynamic  encounter.  It 
is  not  difficult  to  visualize  it,  if  the  spheres  of  attractive 


io6  THE  ORIGIN  OF  THE  EARTH 

force  are  pictured  as  surrounding  the  approaching 
bodies  and  as  plunging  into  one  another.  The  en- 
counter is  very  real,  however  intangible.  The  action 
may  be  pictured  as  a  conflict  of  opposing  attractions; 
or  as  an  overplacing  or  interpenetration  of  attractions; 
or  as  a  neutralization  of  attractions.  In  either  case,  the 


FIG.  9. — Eruptive  prominences  of  the  sun.    Ycrkes  Observatory 

master  body  disrupts  the  minor  body,  or  tends  to  disrupt 
it.  Each  body  stimulates  any  internal  tendency  to  erup- 
tion that  may  affect  the  other  body.  The  matter  that 
may  be  shot  forth  will  be  drawn  into  some  one  of  several 
possible  courses  by  the  joint  attractions  of  the  two 
bodies  whose  positions  and  distances  are  constantly 
shifting. 


DYNAMIC  ENCOUNTER  BY  CLOSE  APPROACH      107 

For  an  illustrative  case,  selected  to  suit  our  problem, 
let  our  sun,  in  its  ancestral  state,  be  the  body  approached. 
For  its  partner  in  action,  let  a  more  massive  star  be 
chosen  and,  for  convenience,  let  it  be  so  dense  and  inert 
that  its  response  to  the  reaction  of  the  sun  upon  it  may 
be  neglected.  In  addition,  it  will  be  convenient  to  speak 
of  the  relative  changes  of  position  of  the  two  as  if  the 
whole  motion  were  made  by  the  passing  star,  though 
in  the  accompanying  illustration  (Fig.  17),  both  bodies 
are  represented  as  moving  about  their  common  center  of 
gravity  as  they  actually  do. 

In  selecting  the  closeness  of  approach,  let  us  observe 
that  only  1/745  of  the  sun's  substance  was  required 
to  form  our  whole  planetary  system.  There  are  now 
known  to  be  eight  planets,  twenty-six  satellites,  and 
about  eight  hundred  planetoids;  probably  the  whole 
number  of  the  latter  may  ultimately  be  found  to  be  a 
thousand  or  so.  The  average  mass  of  these  solar  attend- 
ants is  thus  only  about  1/745,000  of  the  mass  of  the 
sun.  The  average  mass  of  the  planets,  neglecting  the 
planetoids  and  satellites,  is  about  1/6,000.  Even  the 
largest  planetary  mass  is  less  than  a  thousandth  of  the 
mass  of  the  sun.  It  was  not  necessary,  therefore,  that 
the  sun  should  give  forth  even  so  much  as  one-tenth 
of  i  per  cent  of  its  substance  to  form  the  largest  planet, 
assuming  that  the  whole  material  for  the  planet  was 
ejected  from  the  sun  by  a  single  impulse.  The  require- 
ment for  the  earth  would  be  about  one  three- thousandth 
of  i  per  cent  of  the  sun.  It  thus  appears  that  the  draft 
on  the  sun  to  supply  the  substance  of  the  planets  was 
very  small  relatively.  This  suggests  that  the  passing 
star,  if  it  had  the  mass  we  have  chosen,  must  surely  have 


io8  THE  ORIGIN  OF  THE  EARTH 

kept  well  away  from  the  sun  to  have  had  such  slight 
stimulating  effect  as  the  case  required.  We  assume 
therefore  only  a  quite  distant  approach. 

Whether  the  sun  was  more  strongly  eruptive  at  the 
time  the  planets  were  born  than  it  is  now,  or  less  strongly 
eruptive,  is  a  matter  upon  which  perhaps  two  opinions 
may  be  held.  It  does  not  seem  material  to  us  here 
to  know  which  alternative  was  true,  since  the  appropri- 
ate intensity  of  disruptive  effects  could  be  easily  attained 
by  a  nearer,  or  by  a  more  distant,  approach  of  the  passing 
star.  Let  it  be  assumed,  however,  that  the  eruptivity  of 
the  sun  was  of  the  same  order  then  as  now. 

At  present,  the  sun  is  almost  daily  shooting  forth  gas- 
bolts  of  vast  dimensions  and  often  at  such  velocities 
that  they  rise  many  thousands  of  kilometers  above  its 
glowing  surface  (see  Figs.  8,  9,  10,  and  n).  Conserva- 
tive computations  assign  these  eruptive  ejections 
velocities  occasionally  reaching  one  hundred  or  two 
hundred  kilometers  per  second,  though  the  average 
speed  is  less.  Estimates  by  observers  of  high  standing 
assign  much  higher  velocities  in  certain  cases,  some 
of  these  rising  to  several  hundred  kilometers  per  second ; 
indeed,  velocities  that  surpass  the  sun's  power  of  control 
have  been  announced.  But,  in  an  inquiry  that  seeks 
to  keep  well  within  the  bounds  of  probability,  it  is  not 
wise  to  press  the  case  to  its  limits,  and  there  is  no  need  for 
this,  since  extremely  high  velocities  independent  of 
stimulus  are  not  critical  to  the  issue.  Even  if  it  were 
necessary  to  suppose  that  the  eruptions  were  confined 
to  velocities  much  lower  than  the  most  conservative 
interpretation  of  the  observations  would  permit,  it 
would  merely  require  us  to  suppose  that  the  passing  star 


DYNAMIC  ENCOUNTER  BY  CLOSE  APPROACH      109 


FIG.  10. — Eruptive  prominence  of  the  sun  photographed  at  Yerkes 
Observatory  March  25,  1910,  at  4h  14.701. 


FIG.  ii. — Same  prominence  as  above  photographed  March  25,  1910, 
at  4h,  57. 9m,  or  43.2m,  later. 


HO  THE  ORIGIN  OF  THE  EARTH 

came  somewhat  nearer  the  sun  in  evoking  the  ejections 
the  case  requires.  Even  if  the  eruptive  prominences  of 
the  sun  were  essentially  illusions,  eruptive  action  of 
adequate  effectiveness  would  arise  from  a  sufficiently 
near  approach  without  making  serious  drafts  on  the 
full  disruptive  potency  attainable  by  approach.  And 
so,  without  bias  from  any  necessity  of  the  case,  we  are 
free  to  choose  for  our  working  model  such  measure  of  the 
prodigious  eruptive  energies  now  resident  in  the  sun  as 
seems  safest  or  most  probable. 


FIG.  12. — Diagram  of  tidal  forces  showing  lifting  forces  in  due 
proportions  and  directions  to  and  from  the  moon  and  the  girdle  of  com- 
pressivc  forces  at  right  angles  to  these.  Note  that  the  direct  compression 
is  half  that  of  direct  lifting.  Prepared  by  F.  R.  Moulton. 

To  this  group  of  inherent  properties,  energies,  and 
activities,  let  there  now  be  added  the  gravitative  po- 
tencies of  a  great  star  passing  by.  Its  attraction  on 
the  several  parts  of  the  sun  necessarily  differed  because 
of  differences  of  distance.  The  effects  of  the  star's 
attraction  were  of  the  type  made  familiar  by  the  study 
of  the  tides.  Its  differential  attraction  must  obviously 
have  reduced  the  gravitative  pressure  in  the  interior 
of  the  sun  along  the  line  that  joined  the  centers  of  the 
star  and  the  sun;  in  other  words,  there  must  have  been 
a  tidal  elongation.  Let  it  be  recalled  that  such  a  tidal 


DYNAMIC  ENCOUNTER  BY  CLOSE  APPROACH      in 

response  takes  the  form  of  " bulges'7  on  opposite  sides, 
one  toward  the  attracting  body,  and  one  on  the  opposite 
side  (see  Fig.  12).  Between  these  bulges,  and  at  right 
angles  to  their  axis,  there  is  a  girdle  of  tidal  compression 
arising  from  a  component  of  the  oblique  attraction 
exerted  on  these  parts  by  the  tide-raising  body. 

If  the  lifted  portions  that  form  the  " bulges"  were 
plotted  as  though  lifted  from  a  plane,  instead  of  a 


FIG.  13. — Diagram  showing  the  tidal  cones,  A  and  B,  pointing  to  and 
from  the  moon.     Prepared  by  F.  R.  Moulton. 

spheroid,  they  would  appear  as  cones  (see  Fig.  13). 
Such  conical  forms  would  represent  truly  the  way  in 
which  the  lifting  force  of  the  tidal  pull  is  distributed  over 
the  tide-lifted  area.  The  bulging  form,  as  we  style  it, 
arises  from  the  curved  base  on  which  the  lifted  portion  is 
superposed.  There  is  a  certain  merit,  therefore,  in  the 
use  of  the  term  tidal  cones,  rather  than  tidal  bulges. 

Picture  the  passing  star,  therefore,  as  having  eased, 
by  its  differential  attraction,  the  internal  pressure  of  the 


112  THE  ORIGIN  OF  THE  EARTH 

sun  along  the  axis  of  the  tidal  cones,  while  it  has  added 
to  the  pressure  at  right  angles  to  them.  Under  the  law 
of  least  resistance,  it  is  clear  that  this  would  have  pre- 
disposed the  eruptive  forces  within  the  sun  to  ease 
themselves  along  the  lines  of  this  reduced  pressure, 
rather  than  in  directions  of  higher  pressures.  Any 
previous  tendency  to  eruption  at  right  angles  to  the  axes 
of  the  cones  would  necessarily  feel  the  restraint  of  the 
increased  pressure  in  those  directions.  There  would 
therefore  be  a  concentration  and  intensification  of  erup- 
tive action  in  the  axes  of  the  cones  and  a  restraint  and 
reduction  elsewhere.  Even  now,  owing  to  causes  not 
yet  determined,  the  eruptive  action  in  the  sun  is  con- 
centrated in  certain  sub-equatorial  belts.  It  is  also  sub- 
ject to  periodic  fluctuations.  Both  of  these  indicate  its 
susceptibility  to  concentration.  There  is,  therefore, 
firm  ground  for  the  inference  that  the  eruptive  action, 
under  the  conditions  sketched,  would  have  been  centered 
in  the  tidal  cones,  and  would  have  been  much  more 
massive  and  more  forceful  than  under  normal  conditions. 
In  accordance  with  well-known  tidal  principles,  one 
set  of  the  eruptive  projections  must  have  been  shot 
directly  toward  the  passing  star  and  the  other  set  in  the 
opposite  direction.  The  behavior  of  the  latter  is  not 
readily  visualized,  unless  one  has  long  accustomed 
himself  to  see  just  how  each  part  of  the  body  is  moving 
and  what  is  the  balance  of  value  between  its  inertia 
and  the  sum  of  the  attractions  acting  upon  it.  It  is  all, 
however,  a  matter  of  perfectly  consistent  differential 
action  under  the  existent  states  of  motion,  however 
paradoxical  it  may  seem.  The  realities  of  the  case 
are  beyond  question.  For  convenience,  therefore,  let 


DYNAMIC  ENCOUNTER  BY  CLOSE  APPROACH      113 

us  follow  merely  the  outshoot  toward  the  passing 
star,  and  add,  constructively,  in  accordance  with 
demonstrated  mechanics,  the  distal  outshoot.  The 
outshoot  toward  the  passing  star  should  be  a  little 
greater  than  the  outshoot  on  the  farther  side  of 
the  sun. 

The  eruptive  prominences  of  the  sun  are  quite  vari- 
ous in  form  and  dimensions — see  accompanying  figures— 
but  it  is  permissible  to  idealize  them  as  bolts  of  sun- 
substance,  though  the  bolts  must  be  pictured  as 
protean  in  form  and  as  accompanied  by  much  scattered 
material.  A  succession  of  such  bolts,  attended  by 
fragments,  streamers,  and  diversely  scattered  matter, 
naturally  takes  on  the  semblance  of  a  chain  of  eruptive 
projectiles. 

The  initial  course  of  the  gas-bolt,  as  it  left  the  surface 
of  the  sun,  would  be  directly  toward  the  passing  star. 
If  the  attraction  of  the  star  be  for  a  moment  neglected, 
the  bolt,  after  going  out  as  far  as  its  impulse  could  carry 
it,  would  fall  back  to  the  sun,  provided  of  course  that  it 
was  not  shot  entirely  beyond  the  sun's  control.  But 
when  account  is  taken  of  the  attraction  of  the  passing 
star,  the  course  of  the  ejected  mass  is  vitally  dependent 
on  the  precise  balance  of  attractions  and  inertia;  for, 
while  the  bolt  was  moving  out  and  falling  back,  it  would 
have  been  drawn  aside  in  the  direction  of  movement  of 
the  passing  star,  since  the  pull  of  the  star  was  always 
shifting  to  a  new  line  directed  to  its  new  position.  A 
tangential  element  would  thus  be  introduced.  Now  the 
relative  amount  of  this  forward  or  tangential  pull  is  a 
critical  factor;  its  value  is  obviously  dependent  on  the 
relative  distance  to  which  the  bolt  was  projected.  A 


114  THE  ORIGIN  OF  THE  EARTH 

multitude  of  cases  may  arise,  but  they  may  be  grouped 
as  follows: 

1 .  If  the  gas-bolt  were  not  projected  far  out,  relatively, 
it  would  fall  back  to  the  sun  without  being  very  much 
drawn  forward  by  the  passing  star.    It  would,  however, 
in  falling  back  to  the  sun,  carry  such  transverse  momen- 
tum as  it  had  gained  by  the  forward  motion  imparted 
by  the  pull  of  the  star.     This  increment  of  transverse 
momentum  would  affect  the  rotation  of  the  sun,  adding  to 
it,  if  the  sun  were  rotating  in  that  direction;  reducing  it, 
if  the  sun  were  rotating  in  the  opposite  direction;   or 
modifying  it  parti tively,  if  the  sun's  rotation  were  in  an 
oblique  or  transverse  direction.     As  the  sun's  rotation 
is  now  singularly  slow,  and  as  its  axis  is  appreciably 
oblique,  it  is  suggested  that  the  sun's  rotation  may 
originally  have  been  essentially  opposite  to  its  present 
rotation,  and  that  a  series  of  sun-bolts,  shot  out  short 
distances  and  drawn  forward  by  the  passing  star,  in 
falling  back  carried  enough  tangential  momentum  first 
gradually  to  arrest  the  original  rotation  of  the  sun  and 
then  gradually  to  impart  a  slow  rotation  in  the  direction 
pursued  by  the  passing  star.    This  then  may  be  re- 
garded as  the  solar  rotational  group  of  short-distance 
projectiles. 

2.  If  the  gas-bolt  were  shot  a  certain  larger  proportion 
of  the  distance  to  the  passing  star,  the  latter  would 
draw  it  so  far  forward  that,  on  returning  toward  the 
sun,  it  would  fail  to  strike  the  solar  disk;  sweeping  by, 
it  would  fall  into  an  elliptical  orbit  about  the  sun.     If 
the  bolt  were  shot  a  still  larger  part  of  the  distance  to 
the  passing  star,  the  forward  pull  would  be  relatively 
greater,  and,  in  falling  back,  the  bolt  would  give  the 


DYNAMIC  ENCOUNTER  BY  CLOSE  APPROACH      115 

sun  a  wider  berth  and  fall  into  a  more  open  orbit.  And 
so,  by  different  degrees  of  projection,  there  would 
naturally  arise  a  series  of  orbits  of  varying  degrees  of 
eccentricity  and  of  attitude.  This  may  be  regarded 
as  the  planetary  group  of  projectiles,  for  out  of  these 
our  scheme  assumes  that  the  planets  were  aggregated. 

3.  If  the  bolt  were  shot  out  to  a  certain  still  larger 
part  of  the  distance  to  the  passing  star,  the  pull  of  the 
sun  upon  the  bolt  would  be  so  balanced  that  the  course  of 
the  bolt  would  be  veered  into  a  tangent  between  them 
and  elude  the  control  of  either.    This  then  falls  into  the 
group  of  escaping  projectiles;    these  pass  beyond  the 
province  of  our  special  problem. 

4.  If  the  bolt  were  shot  beyond  this  critical  distance, 
it  would  pass  into  the  sphere  of  control  of  the  visiting 
star,  and  would  probably  become  a  secondary  to  it.     In 
a  possible  case,  the  bolt  might  actually  plunge  into  the 
visiting  star,  but  this  would  be  highly  improbable  if  the 
star  were  passing  at  considerable  distance  as  we  have 
supposed.    This  then  represents  a  group  of  projectiles 
that  transfer  allegiance;   they  illustrate  how  stars  may 
gain  or  lose. 

These  are  all  cases  that  arise  from  distant  approaches 
of  a  type  supposedly  fitted  to  our  problem,  and  we  do 
not  need,  in  this  connection,  to  consider  other  cases, 
however  vital  they  may  be  to  a  complete  theory  of  spiral 
nebulae.  But  to  avoid  occasion  for  misapprehension 
because  of  too  complete  neglect,  let  us  note,  before 
passing  on,  not  only  that  much  more  vigorous  eruptive 
and  disruptive  action  would  necessarily  spring  from  the 
closer  class  of  approaches  of  stars  to  one  another,  but  that 
the  positions  of  the  two  stars  relative  to  the  gas-bolts 


n6  THE  ORIGIN  OF  THE  EARTH 

might,  in  some  of  these  cases,  be  rather  radically  different 
from  those  just  considered  and  that  with  such  various 
changes  the  effects  would  be  correspondingly  different. 
In  the  first  two  of  the  four  cases  just  considered,  the 
bolts  are  made  to  turn  backward  before  they  get  half- 
way to  the  star  that  evoked  them.  They  do  not  pass 
outside  the  sun's  sphere  of  control  even  temporarily. 
But,  on  the  other  hand,  if  we  consider  the  cases  in  which 
the  stars  make  very  close  approaches,  it  is  necessary 
to  note,  in  the  first  place,  that  there  is  little  room  between 
the  stars  for  deployment  of  the  kinds  above  sketched  and, 
in  the  second  place,  that  the  eruptions  are  likely  to  be  so 
violent  as  to  project  most  of  the  outshoots  quite  beyond 
this  limited  space  and  introduce  a  new  set  of  cases  of 
extreme  interest  whose  tracing  is  attended  by  extreme 
difficulty.  A  tentative  suggestion  of  their  general 
nature  is  all  that  will  here  be  hazarded: 

a)  If  the  passing  star  curved  close  about  the  sun,  the 
eruptions  would  necessarily  be  violent  and,  being  shot 
directly  toward  the  passing  star,  they  probably  might, 
in  certain  cases,  actually  impinge  upon  it.     In  such  a 
case  the  nebulous  train  on  the  side  of  the  passing  star 
would  actually  connect  it  with  the  eruptive  body,  as 
seems  to  be  suggested  by  M  51  Canum  Venaticorum 
(Fig.  14). 

b)  In  most  cases,  however,  it  seems  probable  that  the 
very  high  speed  of  the  passing  star  in  curving  about 
the  sun  would  carry  it  out  of  the  projectile's  path  before 
actual  impact  could  take  place.    Though  the  projectile 
would  no  doubt  be  much  deflected  toward  the  star,  it 
might  none  the  less  fall  behind  it.     Probably  actual 
collision  of  the  projectile  with  the  evoking  star  would 


DYNAMIC  ENCOUNTER  BY  CLOSE  APPROACH      117 

only  be  imminent  when  either  the  approach  was  ex- 
tremely close  or  the  eruptivityx  of  the  projecting  star 
was  very  intense.  If  the  passing  star  escaped  the  shot 
it  evoked,  as  seems  probable  in  most  cases,  and  the 


FIG.  14. — The  remarkable  spiral  nebula,  M  51,  in  the  constellation 
Canum  Venaticorum.     Photographed  at  the  Yerkes  Observatory. 

projectile,  crossing  the  star's  path  behind  it,  shot  onward, 
both  star  and  sun  would  thereafter  unite  in  restraining 
and  deflecting  its  course  instead  of  contesting  one 
another's  influence  as  in  the  cases  just  previously  con- 
sidered. Very  declared  results,  marked  by  great  diver- 


n8  THE  ORIGIN  OF  THE  EARTH 

gencies  of  paths  and  differences  of  velocity,  might  well  be 
expected. 

With  one  possible  exception,  all  this  group  lie  outside 
the  bounds  of  our  present  problem.  It  is  possible, 
perhaps  not  improbable,  that  a  relatively  small  body- 
passing  near  the  ancestral  sun  evoked  eruptions  of  an 
order  suited  to  the  formation  of  a  planetary  system 
of  the  type  of  our  own.  This  possible  case  throws  the 
chief  burden  of  action  on  the  eruptive  potency  of  the 
sun  and  takes  the  case  essentially  away  from  the  simple 
Roche  principle,  for  in  this  case  a  quite  inferior  body 
supplies  the  stimulus  for  the  eruptive  projection.  The 
elements  of  the  case  are  less  within  the  range  of  celestial 
observations  and  the  dynamics  are  extremely  difficult. 
The  formidable  task  of  tracing  out  such  a  case  has  not 
been  attempted. 

In  general,  however,  the  projectiles  in  cases  of  such 
very  close  approach  might  be  expected  to  be  shot  forth 
very  violently,  to  suffer  great  deflections  in  passing  close 
in  the  rear  of  the  evoking  star,  and  to  pursue  highly- 
varied  courses  and  attain  wide  deployments.  Nebulae, 
so  produced,  are  plausibly  assigned  to  the  giant  class  not 
so  much  because  of  their  massiveness  as  because  of  their 
wide  deployment.  When  really  massive,  they  are  the 
possible  parents  of  star  clusters  or  at  least  of  decentraliza- 
tions of  a  higher  order  than  a  planetary  system  of  the 
solar  type. 

Let  us  return  to  the  simpler  case  whose  elements  we 
have  selected  with  a  view  to  planetary  genesis  by  distant 
stellar  approach.  In  such  simpler  cases  the  logic  of  the 
assigned  movements  seemed  altogether  firm  and  the 
conclusions  inevitable.  But  to  make  these  deductions 


DYNAMIC  ENCOUNTER  BY  CLOSE  APPROACH      119 

doubly  sure,  and  at  the  same  time  to  test,  in  some  measure, 
the  quantitative  value  of  the  deploying  process,  and  to 
determine  the  nature  of  the  orbits  that  would  be  devel- 
oped, Dr.  F.  R.  Moulton,  with  the  computative  aid 


FIG.  15. — Spiral  nebula  HV  2  Virginis.     Photographed  at  the  Lick 
Observatory. 

of  Dr.  E.  J.  Moulton,  followed  out  mathematically  the 
courses  of  representative  units,  projected  in  this  way,  in 
nearly  half  a  hundred  hypothetical  cases.  The  process 
was  found  to  be  unexpectedly  effective;  the  orbits  took 
on  a  wide  range  of  dimensions  as  well  as  much  variety 


120  THE  ORIGIN  OF  THE  EARTH 

of  configuration.  All  the  four  types  of  results  sketched 
in  the  first  list  above  were  encountered  in  the  first  ten 
cases  investigated.  In  his  computative  inquiry,  Dr. 
Moulton  traced  out  the  orbits  of  the  projectiles  shot 
from  the  side  of  the  sun  opposite  the  passing  star,  as  well 
as  those  shot  toward  it.  The  paths  of  the  two  sets  of 
projectiles  were  found  to  be  curved  in  the  same  sense. 

For  obvious  reasons,  the  planes  of  all  such  orbits 
must  lie  in  or  near  the  plane  of  movement  of  the  passing 
star.  The  whole  group  of  orbits  must  thus  take  on  a 
discoidal  configuration  such  as  characterizes  our  plan- 
etary system  and  the  whole  class  of  nebulae  assigned  to 
this  mode  of  origin  (Fig.  16). 

Stars  do  not  pass  near  one  another  in  straight  paths. 
Under  the  law  of  the  heavens,  they  pay  obeisance  to  one 
another  by  deviations  from  their  previous  courses. 
These  usually  describe  hyperbolic  curves.  At  long 
distances,  the  stars  follow  their  normal  courses  with  but 
slight  deviation;  with  closer  approach,  there  is  increas- 
ing curvature  toward  one  another;  when  they  are 
nearest  one  another,  there  is  a  sharper  and  swifter  turn. 
If  the  approach  is  very  close,  their  speeds  at  the  climax 
become  extremely  swift,  and  the  turn  of  the  stars  about 
one  another  correspondingly  sharp.  During  the  stages 
of  closest  approach,  the  positions  of  the  stars  relative 
to  one  another  are  rapidly  changing,  and  hence  the 
tidal  cones  are  constantly  shifting  their  positions  in  the 
sun,  as  well  as  their  directions  in  space.  From  this 
there  arises  inevitably  a  series  of  bolts  shot  out  in  suc- 
cession which  take  new  directions  at  each  successive 
instant.  As  a  mechanical  necessity,  the  chain  of  such 
successive  bolts  takes  the  form  of  a  spiral.  This  may 


DYNAMIC  ENCOUNTER  BY  CLOSE  APPROACH      121 

be  seen  in  detail  by  following  out  the  courses  of  the 
projectiles  represented  in  the  accompanying  diagram 
(Fig.  17).  A  case  of  rather  distant  approach  and  mild 
action,  suited  to  the  development  of  a  small  spiral 


FIG.  16. — Edge  view  of  spiral  nebula  HV  24  Comae  Berenices,  show- 
ing its  highly  discoidal  form.  The  dark  band  is  probably  due  to  light- 
absorbing  nebular  matter.  Photographed  at  the  Lick  Observatory. 

nebula,  was  chosen  for  this  illustration.  It  will  be 
noticed  that  the  paths  pursued  by  the  projectiles  are  not 
identical  with  the  spiral  chain  of  projectiles  into  which 
they  are  forced  to  arrange  themselves.  The  divergence 


122 


THE  ORIGIN  OF  THE  EARTH 


between  the  paths  and  the  chain  of  nebulous  matter 
may  vary  widely.  A  much  closer  approach  to  coinci- 
dence between  the  paths  of  the  projectiles  and  the 
chain  of  projectiles  is  assignable  in  certain  cases  of 
closer  approach  and  more  violent  projection. 


FIG.  1 7. — Diagram  showing  one  of  the  assigned  modes  of  develop- 
ment of  a  spiral  nebula. 


By  such  an  analysis  of  the  consequences  of  the  close 
approach  of  a  massive  body  to  an  eruptive  star,  we  are 
led  to  a  very  definite  concept  of  the  way  in  which  a  spiral 
nebula  may  be  developed.  The  causal  event  is  one  of 
the  simplest  and  most  inevitable.  When  the  multitude 
and  variety  of  the  bodies  subject  to  close  approaches 


DYNAMIC  ENCOUNTER  BY  CLOSE  APPROACH      123 

are  considered,  as  well  as  the  innumerable  degrees  of  pos- 
sible closeness  of  approach,  it  is  clear  that  the  range  of 
effects  may  be  extremely  wide,  and  that  the  maximum 
deployments  may  be  very  impressive.  On  the  other 


FIG.  1 8. — Diagram  showing  an  assigned  mode  of  developing  orbits 
(Moulton). 


hand,  the  milder  effects  must  grade  away  to  the  unrecog- 
nizable. A  great  series  of  spiral  nebulae  ranging  from 
very  wide  deployment  down  to  the  indistinguishable 
seems  to  be  an  almost  necessary  inference  from  the 
nature  of  the  process  and  the  variety  of  the  condi- 
tions. The  nebulae  should,  however,  all  have  a  common 


124  THE  ORIGIN  OF  THE  EARTH 

fundamental  character.  The  multitude  of  spiral  nebulae 
known  to  exist  is  in  close  accord  with  this  deduction. 
The  same  is  true  of  their  variations  in  magnitude  and 
configuration.  If  this  is  the  true  interpretation  of  their 
origin,  it  is  not  at  all  strange  that  they  should  out- 
number all  other  classes. 


THE   TESTIMONY   OF  THE   NEBULAE 

Among  the  distinctive  features  of  the  spiral  nebulae 
are  the  two  arms,  or  groups  of  arms,  that  spring  from 
diametrically  opposite  sides  of  the  nucleus  and  wind 
outward  with  similar  curves,  but  rarely  in  precisely  the 
same  way,  and  almost  never  to  the  same  length.  This 
singular  feature  is  admirably  explained  by  the  assigned 
tidal  genesis.  The  explanation  holds  good  even  to  such 
details  as  the  persistent  inequality  of  the  arms,  and  to 
their  differences  in  configuration. 

It  is  to  be  noted  that  the  arms  must  be  supposed 
to  begin  to  change  their  curvature  more  or  less  as  soon 
as  they  are  projected.  In  so  far  as  a  nebula  is  under 
the  effective  control  of  its  center  of  gravity,  the  inner 
parts  must  move  faster  than  the  outer  ones.  If  the 
residue  of  the  central  mass  remains  large  after  the  arms 
are  thrown  out,  and  these  are  not  projected  far,  speaking 
in  astronomic  terms,  the  arms  must,  after  the  projectile 
motion  is  brought  under  control,  wrap  up  so  closely  in  a 
short  astronomic  period  as  to  be  almost  or  quite  indis- 
tinguishable, at  stellar  distances,  from  a  continuous 
disk.  A  knotted  aspect  might  still  be  presented;  disks 
with  knots  so  in terpre table  are  observed.  Small  spiral 
nebulae  probably  thus  come  to  closely  simulate  planetary 


DYNAMIC  ENCOUNTER  BY  CLOSE  APPROACH      125 


nebulae  in  form,  but  probably  the  spectra  remain  dis- 
tinctive. If,  on  the  other  hand,  the  deployment  of  the 
spiral  is  great  and  the  central  part  has  been  largely  con- 
sumed in  this  deployment,  the  central  gravitative  force 
is  likely  to  be  feeble,  and  its  influence  on  the  revolutionary 


FIG.  i8a. — A  spiral  nebula  in  which  the  two  arms  are  especially 
distinct,  HI  55  Pegasi. 

motion  relatively  unimportant;  the  wrapping,  if  it  ob- 
tains, may  be  extremely  deliberate.  If  the  projection 
is  of  a  still  higher  order,  the  deploying  movement  may 
continue  for  a  long  period. 

If  the  outshoots  from  the  parent  star  are  so  vigorous 
as  to  pass  beyond  the  sphere  of  control  of  the  parent  star, 


126  THE  ORIGIN  OF  THE  EARTH 

or  what  is  left  of  it  after  their  expulsion,  the  projected 
matter  will  normally  not  assume  closed  orbits  about  the 
center  of  the  nebula  but  will  continue  in  courses  diver- 
gent from  it.  This  may  be  one  of  the  modes  of  sowing 
the  germs  of  star  clusters.  Such  uncontrollable  deploy- 
ments probably  only  arise  from  the  very  close  approach 
of  very  massive  bodies  endowed  with  a  very  high 
explosive  competency.  As  repeatedly  noted,  the  genesis 
of  our  planets  is  a  problem  of  a  much  more  modest 
order. 

In  harmony  with  these  variations  of  mass  relations, 
velocities,  and  other  influential  conditions,  the  spiral 
nebulae  present  a  great  variety  of  special  forms,  while 
they  retain,  with  much  fidelity,  the  basal  features  that 
imply  a  decentralizing  process  in  which  a  large  tangential 
or  rotational  element  is  indicated. 

Most  of  the  peculiar  features  of  the  projected  matter, 
its  knots,  blotches,  trails,  and  haze,  seem  to  find  an 
adequate  basis  of  elucidation  as  the  natural  belch- 
products  of  the  solar  eruptions  under  high  external 
stimulus.  An  inspection  of  the  accompanying  photo- 
graphic illustrations  (Figs.  15,  i8a,  19,  20,  25),  with  the 
suggested  genesis  in  mind,  is  invited.  The  illustrations 
are  chosen  almost  necessarily  from  the  larger  varieties  of 
spiral  nebulae,  though  these  do  not  well  fit  the  case  in 
hand.  Small  nebulae,  with  only  scant  and  short  pro- 
jections, such  as  are  suited  to  be  the  parents  of  little 
planetary  systems  like  ours,  are,  with  little  doubt,  nearly 
or  quite  beyond  the  reach  of  the  telescope  at  average 
stellar  distances,  and  besides,  they  probably  wrap  up 
to  scarcely  distinguishable  forms  very  soon  after  forma- 
tion. 


DYNAMIC  ENCOUNTER  BY  CLOSE  APPROACH      127 

The  greatness  of  the  deployment  of  the  giant  spirals 
has  sometimes  been  thought  to  take  them  out  of  the 
category  of  objects  adapted  to  planetary  genesis. 
Quite  likely  their  functions  go  far  beyond  planetary 
genesis  and  include  the  rejuvenation  of  stars  and  the 
formation  of  star  clusters.  But  it  may  be  remarked  that, 
so  far  as  dynamical  requirements  are  concerned,  their 
great  deployment  means  much  less  than  it  gets  credit 
for,  since  all  but  a  small  part  of  the  force  required  for 
the  great  projection  is  consumed  in  the  early  stages 
in  the  vicinity  of  the  parent  star  where  the  opposing 
gravitation  is  effective.  After  the  deployment  has 
reached  the  dimensions  of  a  small  nebula,  only  a  very 
small  additional  percentage  of  the  total  force  is  required 
to  push  the  deployment  to  any  degree  of  dispersion,  even 
indefinite  dispersion. 

The  amount  of  matter  involved  in  the  giant  nebulae 
is  purely  a  matter  of  interpretation.  Nothing  observed 
in  the  heavens  necessarily  implies  great  mass.  On  the 
other  hand,  the  known  masses  of  stars  suggest  great 
possibilities  of  spectacular  impressiveness,  if  properly 
deployed.  They  also  suggest  large  possibilities  of 
producing  germ-suns  ready  to  begin  new  careers  of 
growth.  Jupiter,  though  but  a  thousandth  part  of  an 
average  star,  barely  escaped  being  a  sun.  Judiciously 
divided,  our  sun  might  probably  be  the  parent  of  a 
hundred  germ-suns  ready  for  careers  of  growth.  The 
giant  suns  might  give  rise  to  some  thousands  or  possibly 
tens  of  thousands  of  embryo  suns.  There  seems  no 
cogent  reason,  then,  in  any  known  consideration,  why  a 
star  of  the  larger  order,  vigorously  decentralized  by  very 
close  approach  to  another  massive  body,  may  not  furnish 


128 


THE  ORIGIN  OF  THE  EARTH 


all  the  matter  in  any  of  the  giant  nebulae,  however 
spectacularly  displayed.    The  deep  impressions  formerly 


FIG.  19. — A  strongly  deployed  giant  nebula,  M  33,  in  Triangulum. 
Photographed  at  the  Yerkes  Observatory. 

made   by   the   even   more   spectacular   apparitions    of 
comets  should  perhaps  offer  a  wholesome  suggestion  of 


DYNAMIC  ENCOUNTER  BY  CLOSE  APPROACH      129 

restraint  in  estimating  the  mass-values  of  the  giant 
spiral  nebulae. 

Looked  at  from  the  dynamical  point  of  view,  it  appears 
that  a  little  spiral  nebula,  generated  in  the  way  outlined, 
should  have  the  germs  of  those  extremely  exacting 
dynamical  qualities  which  our  planetary  system  em- 
bodies. The  suggestion  behind  this  is  that  dynamic 
encounter  is  one  of  the  common  and  effective  modes  of 
stellar  rejuvenation. 

SPECIAL  REFERENCE 

1.  Edward  Roche,  Memoire  de  V  Academic  de  Montpcllicr,  Vol.  I. 

GENERAL  REFERENCES 

2.  T.  C.Chamberlin,"On  a  Possible  Function  of  Disruptive  Approach 
in  the  Formation  of  Meteorites,  Comets,  and  Nebulae,"  Astrophysical 
Journal,  XIV  (1901),  17-40;  also  Journal  of  Geology,  IV  (1901),  369-93. 

3.  T.  C.  Chamberlin,  Carnegie  Institution  of  Washington,  Year  Book 
No.  3  (1904),  pp.  208-53. 

4.  T.  C.  Chamberlin  and  R.  D.  Salisbury,  Geology,  II  (1905),  60-80. 

5.  F.  R.  Moulton,  "On  the  Evolution  of  the  Solar  System,"  Astro- 
physical  Journal,  XXII  (1905),  165-81. 

6.  F.  R.  Moulton,  Introduction  to  Astronomy  (1906),  pp.  463-87. 


CHAPTER  VII 

THE  EVOLUTION  OF  THE  SOLAR  NEBULA  INTO  THE 
PLANETARY  SYSTEM 

The  term  solar  nebula  is  not  here  used  in  the  inherited 
sense  of  a  nebula  that  condensed  into  the  sun  and  it> 
attendants,  but  as  a  nebula  evoked  from  the  sun  to  form 
its  attendants.  As  here  interpreted,  the  solar  nebula 
was  little  more  than  a  streaming  knotty  pair  of  arms 
of  nebulous  matter  shot  out  from  the  sun  and  curved 
into  spiral  appendages  about  it  by  the  joint  pull  of  itself 
and  a  passing  star. 

TEST   BY   THE   LAW   OF   PROBABILITIES 

To  give  the  precise  results  actually  realized  in  the  solar 
system,  even  so  simple  a  genesis  as  that  here  assigned 
must  have  involved  the  contributions  of  four  elements, 
each  of  which  might,  theoretically,  have  been  very 
different  from  what  it  actually  was,  and  hence  a  differ- 
ent system  might  have  arisen:  (/)  the  star's  path,  which 
might  have  lain  in  any  direction;  (2)  the  movement  oj 
the  star  in  this  path,  which  might  have  been  either  to  or 
fro;  (j)  the  plane  of  the  sun's  rotation,  which  might  have 
had  various  attitudes,  and  (4)  the  rotation  of  the  sun  in 
this  plane,  which  might  have  been  either  to  or  fro.  It 
would  be  very  remarkable  if  the  path  of  the  star  and  the 
direction  of  its  motion  should  have  concurred  with  the 
plane  of  the  sun's  equator  and  the  direction  of  the  sun's 
rotation.  This,  indeed,  was  one  of  the  multitude  of 

130 


EVOLUTION  OF  THE  PLANETARY  SYSTEM      131 

possibilities  of  the  case,  but  the  probabilities  were 
overwhelmingly  against  it.  The  law  of  probabilities 
would  lead  one  to  expect  such  unconformities  and  dis- 
cordances as  spring  from  random  combinations.  This 


FIG.  20. — A  spiral  nebula  with  large  knots  wrapped  about  a  large 
center.  M  94  (N.G.C.  4736)  Canum  Venaticorum.  Photographed 
at  the  Mount  Wilson  Solar  Observatory. 

seems  to  afford  a  severe  test,  for  our  postulates  can  only 
be  those  which  the  dynamic  vestiges  of  the  system  dictate 
and  the  logic  of  the  case  requires,  and  these  are  rather 
exacting.  They  seem  to  require  (i)  that  the  path  of 


132  THE  ORIGIN  OF  THE  EARTH 

the  star  should  have  lain  nearly,  but  not  quite,  in  the 
invariable  plane  of  the  planetary  system;  (2)  that  the 
movement  of  the  star  in  its  path  should  have  had 
the  direction  in  which  the  planets  now  revolve;  (3)  that 
the  equatorial  plane  of  the  sun  should  have  differed  from 
its  present  plane  to  the  extent  of  the  effects  of  a  certain 
component  of  the  value  of  the  momentum  carried  back 
to  the  sun  by  the  returning  projectiles  after  they  had 
been  drawn  forward  by  the  passing  star,  as  explained  in 
the  last  chapter;  and  (4)  that  the  sun  should  then  have 
rotated  in  a  direction  as  nearly  opposite  to  its  present 
rotation  as  this  change  in  its  plane  permitted,,  the 
reversal  of  the  rotation  being  due  to  the  remaining  com- 
ponent of  momentum  carried  back  by  the  returning 
projectiles.  If  all  these  are  restored  in  imagination,  it 
will  be  seen  that  their  unconformities  are  quite  sufficient 
to  meet  the  demands  of  a  typical  case  of  random  com- 
bination. Indeed,  they  seem  to  imply  about  as  wild  a 
cast  of  the  die  as  the  law  of  chance  could  well  require. 
The  present  degree  of  concurrence  is  a  forced  result  imposed 
by  the  mutual  reactions  of  the  agencies  that  entered  into  the 
combination. 

SPECIFIC   FEATURES   OF   THE   PLANETARY   KNOTS 

'  The  knots  of  the  solar  nebula  play  a  leading  part  in 
our  interpretation  of  the  immediate  genesis  of  the  planets, 
planetoids,  and  satellites,  since  they  served  as  collecting 
centers  for  them.  They  were  not  only  physical  collectors 
but  dynamic  collectors;  they  not  only  arrested  the  flying 
matter  that  fell  into  them,  but,  within  their  spheres 
of  control,  they  drew  flying  matter  toward  the  collecting 
centers  and  made  it  more  liable  to  arrest.  There  was 


EVOLUTION  OF  THE  PLANETARY  SYSTEM     133 

essential  need  for  both  these  functions.  As  a  rule, 
minute  scattered  particles  in  the  open  space  of  the 
heavens  move  faster  than  the  more  massive  bodies. 
They  do  not  "float  in  space,"  but  are  drawn  or  driven 
hither  or  yon  at  more  than  average  velocities.  Where 
space  is  so  dominated  by  the  attractions  of  massive 
stars  and  combinations  of  stars,  where  the  attractions 
of  minute  flying  bodies  are  so  trivial,  and  where  the 
inertia  of  such  flying  particles  is  so  great  relative  to  their 
own  attractions,  the  self -aggregation  of  such  bodies  into 
planets  is  highly  improbable.  The  knots  of  the  nebula, 
however,  furnished  the  requisite  collecting  centers. 

It  would  no  doubt  be  the  part  of  prudence  to  rest 
interpretation  with  this  simple  observation  that  adequate 
centers  of  aggregation  for  our  planets,  planetoids,  and 
satellites  were  offered  by  the  knots  of  the  parent  nebula. 
However,  the  working  value  of  any  hypothesis  depends 
much  on  the  elaboration  of  its  details,  so  that  many  points 
of  contact  with  the  concrete  phenomena  it  is  to  explain 
may  be  presented.  This  must  be  our  excuse  for  offer- 
ing some  speculations  of  rather  uncertain  value  relative 
to  specific  features  of  the  knots  of  the  parent  nebula. 
The  ground  for  this  is  far  from  firm  and  the  suggestions 
should  be  held  lightly,  and  yet  they  may  be  suggestive. 

It  is  assumed  that,  at  the  time  the  nebula  was  formed, 
the  greater  eruptions  of  the  sun  were  concentrated,  as 
now,  in  two  belts  not  far  from  the  sun's  equator.  It 
is  inferred  that,  as  the  star  approached  from  a  distance, 
its  first  feeble  stimulus  led  only  to  moderate  ejectments  of 
sun-substance  and  that  these  suffered  so  slight  deviations 
by  reason  of  the  forward  pull  of  the  star  that  they  did 
not  escape  striking  the  sun's  disk  on  their  return  and  so 


134  THE  ORIGIN  OF  THE  EARTH 

carried  into  the  sun  a  little  momentum  acquired  from 
the  star.  This  momentum  neutralized  an  equivalent 
amount  of  the  momentum  of  the  sun's  rotation,  then 
opposite  to  its  present  rotation.  With  nearer  approach 
of  the  star,  the  eruptions  increased  in  mass  and  vigor 
with  increased  effect  on  the  sun's  rotation.  With  still 
nearer  approach,  a  portion  of  the  projectiles  failed  to 
strike  the  sun's  disk  on  returning  and  swung  into  orbits 
about  it.  Later,  a  still  larger  part  of  the  increasingly 
vigorous  projectiles  passed  into  orbits,  and  these  orbits 
grew  broader,  but  certain  portions  of  the  projectiles  con- 
tinued to  return  to  the  sun  and  affect  its  rotation. 

During  all  this  time  the  pull  of  the  star  was  oblique 
to  the  normal  asccnsive  lines  of  the  sun's  greater  erup- 
tions, and  the  sun  and  star  worked  at  cross-purposes; 
but,  as  the  star  curved  into  the  critical  part  of  its  path, 
where  it  made  its  closest  approach,  it  passed  directly 
over  the  belt  of  the  sun's  most  effective  eruptions,  and 
not  only  the  most  favorable  co-o|>cration  of  sun  and 
star  were  realized  but  nearly  the  maximum  mutual 
attraction.  It  is  assumed  that  the  greatest  eruptive 
bolts  were  then  shot  forth,  and  that  they  were  projected 
with  the  greatest  velocity.  It  is  taken  for  granted  that 
the  stimulus  of  vigorous  action  on  the  side  toward  the 
star  would  react  as  stimulus  to  eruption  on  the  other  side, 
and  that  nearly  simultaneous  bolts  would  issue  from  the 
proximate  and  from  the  distal  side  of  the  sun.  It  is  sup- 
posed that  the  action  would  be  most  effective  when  the 
first  eruptive  belt  was  crossed,  for  then  the  projectile 
forces  drew  on  the  fullest  stores  of  eruptive  potency  in 
the  sun.  The  second  pair  of  great  eruptions  are  assigned 
to  the  stage  when  the  second  belt  of  solar  eruptions,  on 


EVOLUTION  OF  THE  PLANETARY  SYSTEM      135 

the  farther  side  of  the  solar  equator,  was  crossed.  These 
two  pairs  of  eruptive  projectiles  of  the  first  order  are 
assumed  to  have  been  the  parents  of  the  four  great 
planets,  the  two  outermost — with  the  peculiarities  of  the 
first-born — growing  later  into  Neptune  and  Uranus; 
the  two  following,  favored  by  the  pulsations  set  up  by 
the  previous  great  eruptions  and  by  greater  facilities 
for  growth,  but  lacking  the  fullness  of  eruptive  resources 
that  favored  the  first  pair,  constituted  the  knots  that 
grew  into  Saturn  and  Jupiter. 

As  the  star  passed  on  in  its  perihelion  curve  over 
higher  latitudes  of  the  sun,  obliquity  of  action  recurred, 
and  either  a  multitude  of  imperfectly  associated  erup- 
tions, or  a  great  eruption  much  rifted  by  divergent 
projection,  gave  birth  to  many  little  nebulous  bunches 
which  later  grew  into  the  planetoids. 

On  the  backward  swing,  following  the  star's  peri- 
helion turn,  the  passage  over  the  nearest  zone  of  solar 
eruption  was  again  attended  by  a  pair  of  projections, 
but  these  are  supposed  to  have  suffered  greatly  from 
the  measurable  exhaustion  of  the  eruptive  potency  of  the 
sun  involved  in  the  expulsion  of  the  previous  great  bolts 
and  so  attained  only  moderate  masses  and  velocity  of 
projection.  On  passing  the  other  eruptive  belt  the 
second  time,  an  additional  pair  of  bolts  was  shot  out, 
somewhat  smaller  still  and  less  distantly  projected. 
With  this  the  larger  order  of  eruptions  ceased,  and  the 
less  effective  class  of  activities,  such  as  had  attended  the 
early  approach,  was  repeated  in  reverse  order  but,  it  is 
assumed,  with  lessened  vigor  from  progressive  exhaus- 
tion. This  is  a  very  special  explanation  and  obviously 
does  not  apply  to  spiral  nebulae  in  general  because  of 


136  THE  ORIGIN  OF  THE  EARTH 

the  numbers  and  irregularities  of  their  knots.  If  addi- 
tional planets  in  our  system  should  be  discovered,  the 
explanation  would  not  even  hold  for  it. 

INTIMATE  NATURE  OF  THE  KNOTS  AND  NEBULOUS  HAZE 

When  the  immense  belches  of  sun-substance  were 
about  to  be  lifted  from  their  places  deep  in  the  sun, 
they  must  have  been  gaseous  or  potentially  gaseous,  and 
they  must  have  contained  all  the  chemical  substances 
that  were  present  in  the  horizons  of  the  sun  from  which 
they  came.  Nearly  all  the  known  chemical  elements 
were  no  doubt  intimately  intermingled  there,  after  the 
normal  manner  of  gases.  But  when  these  belches 
emerged  from  the  sun  and  were  shot  into  the  approximate 
vacuum  of  surrounding  space,  they  must  have  undergone 
great  expansion,  and  there  must  have  been  a  great 
reduction  of  their  temperature  as  a  consequence.  As 
they  traversed  the  Roche  limit  of  the  sun,  they  felt  a 
modified  form  of  the  Roche  effect  which  intensified 
the  deploying  influences.  When,  after  such  expansion 
and  cooling,  the  nebulous  masses  swept  out  into  inter- 
stellar space  and  entered  upon  their  orbital  courses, 
their  temperatures  suffered  still  further  from  the  rapid 
radiation  inevitable  in  such  diffuse  bodies.  The  vital 
question  arises,  therefore:  How  long  was  the  original 
gaseous  condition  retained  ?  Or  to  what  degree  was  it 
retained  ?  If  it  was  soon  lost,  in  whole  or  in  part,  what 
dynamic  condition  took  its  place  ?  The  answer  is  to  be 
sought  in  the  vestiges  that  remain  for  our  enlightenment, 
if  it  is  possible  to  discern  the  light  that  is  in  them. 

The  great  planets  Jupiter  and  Saturn  have  low 
specific  gravities  and  probably  embrace  high  proportions 


EVOLUTION  OF  THE  PLANETARY  SYSTEM      137 

of  the  more  volatile  elements.  Their  great  masses  give 
them  competency  to  hold  these  in  spite  of  high  molecular 
velocities.  It  is  a  rational  inference  that  the  gas-belches 
from  which  they  sprang  were  also  relatively  massive 
and  gravitatively  competent.  This  is  in  keeping  with 
the  effective  concurrences  to  which  their  birth  is  assigned. 
It  is  assumed,  therefore,  that  at  all  times  in  the  history 
of  the  great  gas-belches  that'  gave  rise  to  Jupiter, 
Saturn,  Uranus,  and  Neptune,  their  self-gravity  was 
competent  to  control  not  only  the  average  planetary 
molecules,  but  the  lightest  and  most  active  molecules 
shot  out  with  them  from  the  sun.  These  great  knots, 
therefore,  probably  had  at  least  gaseous  centers,  even 
when  most  expanded  and  cooled,  and  were  perhaps 
largely  gaseous  bodies  at  all  times.  They  probably 
retained  rather  high  temperatures.  By  reason  of  their 
great  attractive  powers,  they  probably  gathered  in 
effectively  stray  molecules  and  random  aggregates  which 
the  smaller  knots  could  neither  assemble  nor  hold ;  hence 
not  only  their  present  preponderant  masses,  but  their 
relatively  low  specific  gravities. 

In  contrast  to  the  intimations  of  these  great  bodies  of 
low  mean  specific  gravity,  are  the  suggestions  of  the 
planetoids  and  satellites  which  now  hold  little  or  no 
gaseous  envelopes  and  whose  mean  specific  gravities 
are  relatively  high.  The  terrestrial  planets  are  more 
nearly  akin  to  these  than  to  the  great  planets,  so  far  as 
the  gaseous  element  is  concerned.  In  their  present 
full-grown  state,  the  earth  and  Venus  have  fair  atmos- 
pheres; Mars,  a  rather  scant  atmosphere;  Mercury, 
little  or  no  atmosphere.  The  knots  from  which  they 
grew  should  have  been  much  less  competent  to  hold  the 


138  THE  ORIGIN  OF  THE  EARTH 

active  gases,  while  the  high  temperatures  that  attended 
their  emergence  from  the  sun,  by  increasing  the  molecular 
activities  of  the  gases,  further  reduced  their  competency. 
Perhaps  we  need  to  turn  aside  a  moment  here  to 
inquire:  How  much  less  massive  were  the  knots  than  the 
full-grown  bodies  ?  A  considerable  series  of  comparisons 
between  the  apparent  amount  of  matter  in  the  knots 
of  various  spiral  nebulae  and  the  apparent  amount  of 
matter  not  so  bunched  indicates  that  the  knots  may 
perhaps  contain  a  quarter,  a  third,  or  a  half  of  the  whole. 
Considerations  connected  with  the  control  of  the  moon- 
knot  by  the  earth-knot  from  the  outset  seem  best 
satisfied  by  assigning  the  earth-knot  30  or  40  per  cent 
of  the  earth's  adult  mass.  Neither  of  these  estimates 
will  bear  much  emphasis,  for  the  basis  in  both  cases  is 
infirm;  the  light  of  the  nebulae,  by  which  their  masses 
were  judged,  may  not  be  a  safe  guide,  and  the  assump- 
tions of  the  lunar  deduction  are  not  imperative.  The 
estimates  merely  serve  as  a  rough  working  basis.  Duly 
discounted  they  yet  make  it  clear  that  after  the  smaller 
gas-bolts  had  been  shot  from  their  compressed  state 
in  the  sun  into  the  approximate  vacuum  of  interstellar 
space,  their  competency  to  hold  the  more  active  mole- 
cules was  distinctly  limited,  even  in  the  case  of  the 
terrestrial  planets.  So  far  as  concerns  the  little  knots 
that  were  to  grow  into  the  planetoids  and  satellites— 
and  into  Mercury  and  Mars  as  well — it  may  be  con- 
cluded with  confidence  that  such  gases  as  now  form 
our  atmosphere  could  not  have  been  held  under  control  at 
the  high  temperatures  at  which  they  were  shot  from  the 
sun.  The  light  active  molecules  that  mingled  in  these 
smaller  gas-bolts  must  probably,  as  they  issued  into 


EVOLUTION  OF  THE  PLANETARY  SYSTEM      139 

open  space,  have  been  scattered  hither  and  yon  by  the 
force  of  their  own  collisional  reactions,  and  must  have 
entered  on  paths  of  their  own  under  the  direct  control  of 
the  sun,  but  free  from  the  control  of  the  bolts  with  which 
they  were  shot  forth.  If  so,  they  no  longer  constituted 
bodies  of  gas  in  the  true  kinetic  sense.  In  following 
orbital  paths  about  the  sun,  they  had  the  dynamic 
qualities  of  little  planets,  that  is,  they  were  planetesimals. 
This  name  has  been  introduced  to  designate  all  such 
small  bodies — whether  atoms,  molecules,  or  aggregates— 
as  behave  like  minute  planets.  This  is  done  to  dis- 
tinguish them  from  the  constituents  of  gases,  from  most 
meteorites,  and  from  other  minute  bodies  that  follow 
heterogeneous  paths  and  that  have,  as  a  result,  different 
dynamic  qualities. 

Contrasted  with  the  escape  of  very  light  active  mole- 
cules from  the  smaller  knots,  was  the  tendency  of  the 
heavy  sluggish  molecules,  and  of  such  aggregates  as 
may  have  been  formed,  to  remain  assembled  under  their 
own  mutual  gravity.  The  mean  specific  gravity  of  the 
moon  is  3.4;  that  of  the  earth  5.5;  that  of  Mars, 
Mercury,  the  planetoids,  and  the  satellites  generally,  so 
far  as  determined,  of  the  same  general  order.  A  part 
of  this  high  specific  gravity  is  due  of  course  to  com- 
pression, but  aside  from  this  their  inherent  specific 
gravity  is  high.  It  is  easy  to  be  misled  as  to  the  average 
specific  gravity  of  earth-substance.  The  atmosphere 
and  the  hydrosphere  make  a  brave  show  at  the  surface- 
whence  we  are  compelled  to  view  the  earth — but  they 
really  constitute  only  a  trivial  fraction  of  earth-substance. 
The  great  mass  of  the  earth  is  made  up  of  much  heavier 
substances,  and  it  is  the  behavior  of  these  heavy 


140  THE  ORIGIN  OF  THE  EARTH 

substances  that  constitutes  the  essence  of  our  present 
problem.  Few  of  these  substances  could  remain  volatile 
except  at  very  high  temperatures.  Hence  on  emerging 
from  the  sun  and  undergoing  the  great  expansions  and  the 
effective  radiations  incident  to  this,  a  large  portion  of 
the  more  refractory  material  in  the  smaller  order  of 
knots  probably  fell  to  the  liquid  or  solid  state.  In  the 
discrete  state  that  ensued,  combined  with  the  influence 
of  their  projectile  impetus,  the  assemblage  of  particles 
could  scarcely  collapse  as  a  unit ;  the  particles  could  prob- 
ably only  coalesce,  with  such  other  particles  as  crossed 
their  paths,  into  minute  scattered  aggregates,  or  else 
remain  as  independent  molecules.  In  so  far  as  any 
matter  of  this  heavier  order  remained  in  a  free  molecu- 
lar state,  its  activity  would  have  been  of  the  lower 
order.  It  is  inferred,  therefore,  that  the  smaller  knots 
were  formed,  in  large  proportion,  of  minute  discrete 
particles,  or  of  heavy  molecules,  and  that  these  largely 
followed  individual  paths  of  the  orbital  type,  instead 
of  remaining  in  collisional  interaction  of  the  gaseous 
type. 

While  the  projectile  force,  as  well  as  the  rotatory 
impulse  incident  to  the  expulsion  of  the  eruptive  belches, 
stood  in  the  way  of  a  direct  concentration  of  the  knots, 
it  is  assumed  that  their  dispersive  effect  failed  to  prevent 
a  certain  considerable  portion  of  the  heavier  material 
from  remaining  under  the  control  of  its  own  self -gravity. 
The  existence  of  knots  seems  to  imply  this.  This 
self-controlled  portion  constituted  the  real  knot  in  the 
dynamic  sense.  Whatever  part  of  the  primitive  bolt 
escaped  from  this  control  and  scattered,  was  drawn  into 
independent  orbits  about  the  sun  and  became  planetesi- 


EVOLUTION  OF  THE  PLANETARY  SYSTEM      141 

mals.  Soon  after  emergence,  then,  most  of  the  nebulous 
matter  is  supposed  to  have  either  been  gathered  into 
knots,  the  collecting-centers  of  the  future  planets, 
planetoids,  and  satellites,  or  into  planetesimals,  the 
food  on  which  these  knots  subsequently  fed. 

Gathering  these  postulated  results  together,  they 
form  a  graded  series : 

At  the  head  were  eruptive  actions  of  the  first  order 
whose  bolts  were  massive  enough  to  retain  strong 
gravitative  control  of  themselves  and  be  able  to  gather 
and  hold  very  volatile  as  well  as  heavy  matter.  They 
hence  had  great  powers  of  growth  and  became  giant 
planets. 

Next  in  order  were  bolts  of  inferior,  but  yet  consider- 
able, mass  from  which,  at  the  high  temperature  of 
emergence,  the  most  highly  active  molecules  largely 
escaped,  but  the  heavier  and  less  active  remained,  and 
this  selected  portion  constituted  the  material  for  the 
next  stage  of  segregation. 

Next  below  these  came  a  much  larger  number  of 
notably  smaller  bolts,  most  of  them  independent  of  the 
larger  knots,  some  of  them  secondary  to  larger  knots. 
In  most,  if  not  in  all,  of  these,  the  mass  was  insufficient 
to  hold  atmospheric  and  hydrospheric  material  at  the 
temperature  of  ejection  from  the  sun,  and  rarely 
even  at  the  much  lower  temperatures  of  open  space. 
These,  therefore,  soon  came  to  be  merely  swarms  of 
heavy  molecules  and  of  aggregates;  yet  they  had  self- 
gravity  enough  to  hold  themselves  in  an  assembled 
state. 

Below  all  these  there  were  the  scattered  products  of 
dispersive  action,  embracing  free  molecules  and  small 


142  THE  ORIGIN  OF  THE  EARTH 

aggregates.  These  very  generally  were  thrown  into 
orbits  of  the  planetary  type  and  constituted  planetesi- 
mals. 

CORES  OF  KNOTS  OF  MEDIUM  MASS 

The  status  of  the  largest  order  of  knots  is  clear,  for 
they  could  hold  the  more  active  molecules,  even  hydro- 
gen and  helium.  The  status  of  the  smallest  order  of 
knots  was  also  clear,  for  they  could  not  hold  appreciable 
quantities  of  free  nitrogen,  oxygen,  and  water- vapor. 
The  status  of  the  knots  of  the  intermediate  order,  that 
were  to  form  the  terrestrial  planets,  was  more  doubt- 
ful. There  is  little  reason  to  suppose  that  the  cores 
of  the  knots  of  the  two  smallest  planets,  Mercury  and 
Mars,  held,  in  a  free  state,  any  notable  amount  of  the 
atmospheric  gases,  since  the  full-grown  planets  show 
only  scant  powers  of  holding  material  of  such  high 
molecular  activity.  Very  likely  they  may  have  had 
cores  formed  of  heavier  molecules  in  a  gaseous  or  semi- 
gaseous  condition.  The  knots  of  the  earth  and  Venus 
quite  probably  had  the  power  of  holding  the  atmospheric 
gases — if  these  escaped  absorption  or  combination  with 
the  multitude  of  minute  aggregates  of  the  knots — after 
their  temperatures  fell  to  about  that  of  their  present 
surfaces.  Earlier  than  this,  when  they  were  much 
hotter  from  recent  emergence  from  the  sun,  their  com- 
petency is  more  doubtful.  The  balance  of  probabilities 
seems  to  favor  the  view  that  the  knots  of  Venus  and  the 
earth  were  formed  chiefly  of  heavy  refractory  material 
assembled  largely  in  an  orbital  state  around  a  core  of 
gaseous  or  semi-gaseous  matter  of  heavy  molecules  and 
that  there  were  mingled  with  both  these  parts  con- 
siderable atmospheric  material. 


EVOLUTION  OF  THE  PLANETARY  SYSTEM      143 
SPECIFIC    ORIGIN    OF    SATELLITES    AND    SATELLITESIMALS 

It  is  assumed  as  inevitable  that  the  main  ejected 
masses  should  have  been  attended  by  fragments  or  sub- 
knots  torn  from  them  as  they  were  belched  violently 
forth.  It  seems  equally  inevitable  that  there  should 
have  been  different  intensities .  of  the  eruptive  force 
propelling  the  escaping  bolt,  beneath  one  part  or  another, 
so  that  rotation  of  the  ejected  mass  was  unavoidable. 


FIG.  21. — An  eruptive  prominence  of  the  sun  showing  ragged  borders 
and  a  tendency  to  minor  bunchings.  Photographed  at  the  Yerkes 
Observatory. 

The  extreme  vigor  of  the  expulsory  action  gives  ground 
for  supposing  that  the  rotatory  motion  had  appreciable 
value.  The  relations  between  the  time  and  the  move- 
ment of  the  tidal  cones  drawn  forth  by  the  passing  star 
were  no  doubt  important  factors  in  determining  »the 
direction  of  rotation  of  the  knots,  for  pulsations  doubt- 
less lingered  in  the  spot  from  which  the  previous  belch 
was  shot  and  this  affected  the  eruption  that  followed 


144  THE  ORIGIN  OF  THE  EARTH 

on  the  advancing  side.  The  particular  conjunction  of 
these  movements  postulated  at  the  opening  of  this 
chapter  is  believed  to  have  been  favorable  to  that  type 
of  rotations  which  the  adult  planets  now  embody. 

While  these  fragments  or  sub-knots  were  shot  out 
with  the  principal  masses,  it  was  inevitable  that  there 
should  be  divergencies  which  gave  them  separate 
courses  near  the  main  masses,  which  resulted  in  revolu- 
tions about  these  masses  when  their  control  was  compe- 
tent. They  thus  became  attendant  or  satellite  knots. 
Fragments  whose  courses  were  too  divergent  or  too 
swift  of  course  escaped.  It  is  thus  assumed  that  the 
collecting  centers  of  the  satellites-to-be  originated  as 
incidents  of  the  vigorous  ejection  of  the  primary 
knots. 

While  the  highest  order  of  knots  probably  always 
had  large  hot  gaseous  centers,  in  spite  of  expansion  and 
radiation  on  emergence  from  the  sun,  the  outer  portion 
of  their  spheres  of  control  should  have  been  occupied, 
in  very  open  fashion,  by  ultra-atmospheres  of  molecules 
pursuing  orbital  courses,  as  set  forth  in  the  first  chapter. 
Probably  there  were  also  minute  aggregates  derived  from 
the  nebula  pursuing  similar  orbits  in  this  outer  portion. 
All  these  orbital  bodies  were  of  the  nature  of  minute 
satellites,  that  is,  satellitesimals,  for  they  revolved  about 
the  centers  of  knots  that  were  to  form  planets.  Some 
notable  part  of  the  material  of  the  planetary  knots  may 
have  been,  made  up  of  these  satellitesimals.  They 
probably  served  an  important  function  in  the  evolution 
of  the  final  state  of  the  satellites  and  of  the  planets 
as  well,  for  they  were  dynamic,  as  well  as  material,  food 
for  both. 


EVOLUTION  OF  THE  PLANETARY  SYSTEM      145 

While  such  a  degree  of  specific  postulation  may  not 
unjustly  be  regarded  as  pressing  deduction — or  specula- 
tion, if  you  please — to  great  lengths,  this  may  perhaps  be 
pardoned  in  so  far  as  it  gives  a  definite  picture  of  the 
working  essentials  of  the  planetesimal  hypothesis  in  its 
closest  application  to  planetary  origin,  for,  given  these 
postulates,  the  rest  of  the  evolution  is  predetermined 
by  the  mechanics  of  the  case.  These  specific  pictures 
are  indeed  little  more  than  attempts  to  interpret  the 
physical  and  dynamical  vestiges  now  embodied  in  our 
planetary  system  by  projecting  these  backward  to  their 
initial  states.  It  goes  without  saying  that  these  deduc- 
tions are  tentative,  and  that  they  will  quite  surely  need 
emendation  when  the  vestiges  that  are  their  source 
shall  be  better  read  and  more  successfully  traced  to  their 
antecedent  states. 

AGGREGATION   OF   THE   NEBULOUS   MATTER 

Three  processes  are  believed  to  have  formed  the 
essential  features  of  the  concentration  of  the  nebulous 
matter  into  planets,  planetoids,  and  satellites:  (i)  the 
direct  condensation  of  the  gaseous  centers  of  the 
knots,  where  there  were  such,  into  liquid  or  solid  cores; 
(2)  the  less  direct  and  slower  collection  of  the  orbital 
or  satellitesimal  particles  of  the  knots  into  solid 
cores;  and  (3)  the  still  slower  gathering  of  the  plane- 
tesimals  into  the  knots  or  through  these  into  solid 
cores. 

i .  The  condensation  of  the  heavy  vapors  of  the  smaller 
knots  should  have  been  direct  and  rapid.  In  the  giant 
knots,  condensation  doubtless  proceeded  more  deliber- 
ately, both  because  of  the  slower  loss  of  heat  and  because 


146  THE  ORIGIN  OF  THE  EARTH 

of  the  larger  presence  of  highly  volatile  and  uncondens- 
able  gases.  In  knots  of  the  intermediate  terrestrial 
class,  the  heavy  vapors  doubtless  condensed  rather 
rapidly,  while  the  highly  volatile  and  irreducible  gases 
gathered  into  atmospheres  about  the  nuclei  or  cores. 

2.  The  gathering  of  the  orbital  part  of  the  knots,  the 
satellitesimals,  into  the  planetary  and  satellite  cores, 
was  doubtless  a  slower  process,  for  it  depended,  in  part, 
on  the  collision  of  the  satellitesimals  with  one  another 
in  their  orbits — which  would  take  place  only  in  so  far  as 
these  crossed,  or  were  made  to  cross,  one  another — and, 
in   part,   on   collisions   with   infalling   planetesimals — 
which  either  drove  them  into  the  nucleus  or  into  new 
orbits  from  which  sooner  or  later  a  plunge  into  the  nucleus 
would  be  likely  to  ensue.    A  planetesimal  plunging  into  a 
satellitesimal  would  drive  it  into  the  nucleus  in  only  a 
certain  proportion  of  cases,  but,   under  the  laws  of 
mechanics,  both  planetesimal  and  satellitesimal  must 
return  to  the  point  of  collision — unless  diverted  by  some 
intercurrent  agency  or  prevented  by  too  high  velocity— 
and  be  subject  to  another  collision  which  would  give 
another  chance  of  being  deflected  into  the  nucleus,  and 
so  on  indefinitely. 

3.  It  appears  then  that  the  orbital  or  satellitesimal 
deployment  of  the  particles  of  the  knots  served  not  only 
as  a  slow  source  of  feeding  for  the  nucleus  or  core,  but 
also  as  a  collecting  mechanism  for  catching  planetesimals; 
so  also,  in  reciprocity,  the  planetesimals  aided  in  driving 
in  the  satellitesimals.     In  some  measure,  indeed,  the 
whole  of  the  sphere  of  gravitative  control  surrounding 
each  knot  served  as  a  collecting  agency  by  reason  of  its 
power  of  deflecting  passing  particles  toward  the  center 


EVOLUTION  OF  THE  PLANETARY  SYSTEM      147 

and  thus  increasing  their  liability  to  be  caught.  But 
the  process  of  aggregation  was  none  the  less  slow. 

If  now  the  earlier  picture  of  the  mode  by  which  the 
passing  star  diverted  the  solar  projectiles  into  orbital 
paths  about  the  sun  be  recalled  in  its  details,  it  will 
appear  that  the  movements  of  knots  and  planetesimals 
were  all  in  the  same  direction.  A  few  of  the  satellite 
knots  and  satellitesimals  might,  indeed,  have  moved, 
and  did  move,  in  the  opposite  direction,  but  these 
are  here  negligible,  though  important  in  other  relations. 
The  fall  of  planetesimals  into  the  knots  came  then  from 
overtakes  in  paths  that  were  similar.  The  impacts 
must  often  have  been  rather  sharp,  as  we  measure 
impacts  in  terrestrial  matters,  but  they  were  relatively 
mild  in  the  celestial  sense,  and  the  generation  of  heat 
as  a  consequence  was  relatively  small.  There  does  not 
seem  to  be  any  cogent  reason  for  assuming  that  molten 
planets  would  arise  from  this  mode  of  aggregation, 
except  in  those  cases  in  which  the  knots  were  very  large. 

If  we  recall  again  the  generation  of  the  nebula,  it  will 
appear  that,  while  all  the  orbits  of  the  knots  and  the 
planetesimals  were  elliptical,  there  was  much  variation 
in  the  degrees  of  ellipticity  and  in  the  dimensions  of  the 
orbits.  The  orbits  were  hence  generally  unconformable 
to  one  another,  in  some  degree,  and  the  crossings  of 
paths  were  many  and  various.  These  crossings  were 
all  the  more  prevalent  because  nearly  all  the  orbits  lay 
in,  or  near,  a  common  plane  determined  by  the  passing 
star.  These  crossings  were  vital  features  in  promoting 
aggregation.  The  fact  that  all  the  bodies  in  these 
intertangled  orbits  were  moving  in  the  same  general 
direction  and  at  rates  not  radically  different  gave  time  for 


148  THE  ORIGIN  OF  THE  EARTH 

gravitative  action  with  minimum  resistance  to  gravita- 
tive  pulls.  These  conditions  were  also  favorable  for 
electric  and  magnetic  action.  These  were  liable  to  be 
more  effective  than  gravitation  in  their  effects  on 
minute  bodies.  At  present,  too  little  is  known  of  the 
electric  and  magnetic  states  in  the  heavens  to  warrant 
confident  deductions,  but  it  is  prudent  to  recognize 
them  as  factors  of  probable  importance. 

The  sweeping  of  the  nebular  haze  into  the  knots  was 
aided  by  the  shifting  of  the  orbits  of  both  knots  and 
planetesimals.  This  shifting  arose  inevitably  from  their 
mutual  attractions,  just  as  the  orbits  of  the  planets  now 
shift  by  reason  of  planetary  attractions.  Thus  fresh 
opportunities  for  collisions  and  close  approaches  were 
being  evolved  as  time  went  on. 

Furthermore,  as  the  knots  grew,  the  form  of  their 
orbits  changed  as  a  consequence  of  the  accession  of 
planetesimals.  These  new  orbits  cut  the  orbits  of  the 
remaining  planetesimals  in  new  ways  with  new  possi- 
bilities of  conjunction.  Thus  the  process  was  helped  on 
by  the  very  results  of  its  own  progress. 

However  much  the  process  of  gathering  the  scattered 
matter  into  the  planetary  cores  was  aided  by  these 
auxiliaries,  it  was,  as  already  remarked,  slow.  Inspec- 
tion shows  that  the  chance  of  any  particular  planetesimal 
falling  into  any  given  planetary  nucleus  was  very  small 
compared  with  the  chances  of  escaping  and  continuing 
in  its  own  independent  career.  In  the  alternative 
between  a  free  life  as  a  planetesimal  and  absorption 
into  the  larger  life  of  a  planet,  planetoid,  or  satellite, 
the  statistical  allotment  of  chances  was  such  as  to  give 
the  larger  share  to  the  former  in  any  given  short  epoch. 


EVOLUTION  OF  THE  PLANETARY  SYSTEM      149 

In  the  average  case,  the  absorption  was  long  delayed. 
This  slowness  of  growth  vitally  conditioned  the  physical 
states  of  the  planetary  cores  in  their  early  history,  a 
subject  of  peculiar  interest  in  the  case  of  the  earth,  which 
will  claim  attention  in  the  next  chapter. 

EVOLUTION  OF  CIRCULARITY  OF   ORBITS 

When  a  multitude  of  bodies  moving  in  eccentric 
orbits  of  like  type  coalesce  into  one  body,  the  resulting 
orbit  is  almost  necessarily  more  circular  than  the  most 
eccentric  of  the  previous  orbits;  it  is  likely  to  be  more 
circular  than  the  majority  of  them ;  it  may  even  be  more 
circular  than  any  of  them.  In  sketching  the  origin  of 
the  orbits  of  the  knots  and  planetesimals,  it  was  noted 
that  there  was  a  progressive  broadening  of  the  elliptic 
orbits  until  their  greater  extensions  came  to  be  trans- 
verse to  those  of  the  first-formed  orbits.  Furthermore, 
there  were  two  sets  of  orbits,  one  on  each  side  of  the 
sun.  Developed  in  this  way,  there  was  a  strong  pre- 
sumption that  the  coalescence  of  a  vast  multitude  of 
planetesimals  in  building  up  each  knot  into  a  planet, 
planetoid,  or  satellite  would  give  the  mass  an  orbit 
much  more  nearly  circular  than  either  the  average 
plane tesimal  or  the  knot  had  possessed  before.  The 
principles  of  such  combinations  are  illustrated  in  Figs.  22 
and  23.  While  these  are  selected  cases  and  somewhat 
specially  favorable  perhaps,  they  yet  fairly  represent 
the  tendency  of  aggregation  to  produce  circularity. 

In  support  of  this,  it  is  interesting  to  note  that  the 
orbits  of  the  four  great  planets — which  must  probably 
have  grown  most — are  more  nearly  circular,  on  the 
average,  than  those  of  the  terrestrial  planets — which 


THE  ORIGIN  OF  THE  EARTH 


should  have  grown  less — and  that  the  orbits  of  these, 
in  turn,  are  more  nearly  circular,  on  the  average,  than 
the  orbits  of  the  planetoids  which  probably  grew  still 
less. 


FIG.  22.— Diagram  to  illustrate  the  tendency  toward  circularity 
when  the  orbits  of  the  uniting  bodies  have  concentric  positions.  The 
two  bodies  revolving  in  the  orbits  A  and  B,  and  uniting  at  D,  necessarily 
take  an  intermediate  orbit,  C,  with  an  obvious  advance  toward  circu- 
larity. In  less  simple  and  symmetrical  cases,  the  result  is  less  obvious, 
but  it  would  be  of  the  same  order  in  ail  cases  involved  in  the  problem  in 
hand. 

SPACING  OF  THE  PLANETS 

In  the  earlier  part  of  this  chapter,  the  original  spacing 
of  the  planetary  knots  was  assigned  to  the  different 
degrees  of  force  of  projection  that  arose  from  the  changing 
relations  of  sun  and  star  and  from  the  progressive 


EVOLUTION  OF  THE  PLANETARY  SYSTEM      151 

exhaustion  of  eruptive  resources.  Given  this  primary 
distribution,  a  secondary  influence  began  to  work  to  in- 
duce a  higher  degree  of  regularity.  Let  it  first  be  noted, 
however,  that  it  is  easy  to  over-emphasize  the  degree 
of  regularity  that  actually  obtains.  Clearly  this  has  been 
done  in  the  attempts  to  make  the  spacing  of  the  planets 
appear  as  an  expression  of  "  mathematical  law."  The 
semblance  of  a  law  only  appears  after  there  has  been 


FIG.  23. — Diagram  to  illustrate  the  evolution  of  circularity  where 
the  orbits  of  the  uniting  bodies  are  as  far  as  possible  from  having  con- 
centric positions.  The  bodies  in  the  orbits  A  and  B,  meeting  and  uniting 
at  D,  necessarily  take  an  intermediate  orbit  C,  which  is  obviously  more 
circular  than  either.  In  less  symmetrical  cases,  the  tendency  would 
be  of  the  same  order. 

suitable  preliminary  trimming  of  the  facts  of  distribution, 
and  even  then  the  effort  is  made  seemingly  successful  only 
by  overlooking  a  bad  break  in  one  of  the  eight  items 
involved.  None  the  less,  the  spacing  is  sufficiently  sub- 
regular  to  require  consideration. 

If  any  planet  grew  most  from  planetesimals  moving 
in  orbits  larger  than  its  own,  its  orbit  would  have  been 
enlarged;  if  it  grew  most  from  planetesimals  in  smaller 


152  THE  ORIGIN  OF  THE  EARTH 

orbits,  the  reverse.  If,  therefore,  the  planetesimals 
were  evenly  distributed,  and  if  two  of  the  planetary 
knots,  at  the  beginning  of  their  growth,  happened  to  have 
orbits  close  to  one  another,  while  on  the  opposite  sides 
there  were  wider  spaces,  the  two  knots  would  add  less 
matter  to  themselves  from  the  narrow  space  between 
them,  for  which  they  were  competitors,  than  from  the 
ampler  space  on  the  opposite  sides  where  the  feeding- 
ground  was  more  largely  their  own.  As  a  mechanical 
necessity,  they  would  move  apart.  In  the  course  of  a 
growth  involving  probably  more  than  half  the  total 
mass  of  the  planets,  this  automatic  adjustment  should 
probably  have  had  an  appreciable  value,  modifying 
the  original  spacing  of  the  planetary  nuclei. 

If  Neptune  grew  from  the  knot  that  was  projected 
farthest  from  the  sun,  there  should  have  been  little 
scattered  matter  beyond  it  to  be  gathered  in  on  its  outer 
side,  while  not  a  little  may  have  fallen  somewhat  short 
and  have  been  gathered  in  later  on  its  inner  side.  In 
this  case,  the  Neptunian  orbit  shrank  as  the  planet  grew, 
and  this  may  be  why  its  orbit  falls  far  short  of  the  posi- 
tion assigned  it  by  Bode's  formula. 

GROWTH  AND  ADJUSTMENT  OF  THE  SATELLITES 

The  growth  of  the  satellites  from  secondary  knots  is 
presumed  to  have  followed  the  same  general  lines  as  the 
growth  of  the  planets  from  the  primary  knots,  but 
certain  special  features  call  for  comment.  All  satel- 
lites, as  a  necessity  of  their  continuance  as  satellites, 
revolve  within  the  spheres  of  control  of  their  primaries. 
In  view  of  this,  it  is  assumed  that  the  satellite  knots  left 
the  sun  within  the  spheres  of  control  of  their  primaries 


EVOLUTION  OF  THE  PLANETARY  SYSTEM      153 

and  that  they  always  remained  within  them.  A  cap- 
tured satellite,  while  perhaps  not  an  impossibility,  should 
bear  distinct  earmarks  of  its  exotic  origin. 

Each  of  the  large  families  of  satellites  is  assembled  in  a 
disk  in  or  near  the  plane  of  the  planet's  equator.  The 
configurations  of  these  satellite  families  are  very  similar 
to  that  of  the  planetary  family,  with  a  single  notable 
exception.  There  are  no  retrograde  planets,  and 
theory  provides  for  none;  but  three  retrograde  satel- 
lites have  recently  been  discovered,  and  theory  pro- 
vides for  these.  In  addition  to  these,  there  are  the 
highly  oblique  satellites  of  Uranus  and  Neptune,  but 
these  perhaps  belong  to  a  somewhat  different  type. 
The  rotations  of  the  planets  Uranus  and  Neptune  are 
not  known.  Their  satellites  probably  revolve  har- 
moniously with  them.  However  this  may  be,  the 
satellite  orbits  are  highly  oblique  to  the  invariable  plane 
of  the  planetary  system  and  may  be  regarded  as  retro- 
grade. This  attitude  is  perhaps  assignable  to  the  mode 
of  escape  of  the  parent  knots  from  the  sun.  If  these 
knots  were  the  products  of  the  first  great  eruptions 
from  the  opposite  sides  of  the  sun,  their  rotations  were 
uninfluenced  by  prior  great  eruptions  and  the  law  of 
chance  was  applicable  to  them;  this  they  fairly  satisfy. 
The  great  belches  that  came  later  may  have  been  much 
influenced  by  the  pulsations  that  long  followed  the 
ejection  of  their  predecessors.  At  any  rate,  the  rotations 
of  Jupiter  and  Saturn  are  forward  and  quite  swift; 
they  give  no  hint  of  instability  or  reversal.  Both 
Jupiter  and  Saturn  have  goodly  families  of  satellites 
that  revolve  in  harmony  with  themselves.  Yet  Jupiter 
has  two  moons  that  revolve  in  a  retrograde  direction, 


154 


THE  ORIGIN  OF  THE  EARTH 


and  Saturn  has  one.  Under  the  plane tesimal  view  this 
is  interpreted  to  mean  that  the  larger  part  of  the  frag- 
menting action  about  the  borders  of  the  great  belches 
that  sent  forth  the  Jovian  and  Saturnian  knots  was 
actuated  by  the  great  impulses  that  gave  rotation  to  the 


FIG.  24. — An  eruptive  prominence  of  the  sun  showing  a  series  of 
sub-knots  projected  with  the  main  knot.  Photographed  at  the  Yerkes 
Observatory. 


primary  knots,  but  yet  that  minor  fragmenting  outbursts 
occurred  on  the  opposite  side  and  gave  rise  to  secondary 
knots  with  retrograde  revolutions.  These  probably 
succeeded  in  maintaining  themselves  because  they  were 
far  out  where  orbital  matter  was  scant,  and  the  amount 


EVOLUTION  OF  THE  PLANETARY  SYSTEM      155 

they  encountered  was  limited.  As  anticipated  by 
Moulton,  from  the  mechanics  of  the  case  before  their 
discovery,  their  orbits  are  notably  eccentric  and  the 
planes  of  their  orbits  divergent  from  the  equatorial 
planes  of  their  primaries. 

These  anomalies  aside,  the  distinctly  harmonious 
relations  of  the  other  satellites,  the  great  majority,  is 
so  notable  as  to  imply  an  efficient  cause.  The  primary 
basis  for  harmony  probably  lies  in  the  fact  that  the 
impulse  which  gave  the  planetary  knots  their  initial 
rotations  also  gave  the  secondary  knots  their  revolutions. 
The  same  impulse  should  also  have  determined  the  planes 
of  revolution  of  the  multitude  of  more  minutely  frag- 
mented bodies  that  were  driven  forth  by  the  same  blast 
and,  like  the  satellite  knots,  revolved  about  the  plane- 
tary centers,  that  is,  the  satellitesimals.  Beside  such 
inheritances  from  the  original  ejection,  there  should 
have  developed  perpetually  an  orbital  ultra-atmosphere 
about  each  competent  knot  in  the  manner  set  forth 
in  the  first  chapter.  This  should  have  been  a  perpetual 
dynamical  tie  between  the  orbital  portion  of  the  knots 
and  the  cores,  and  should  have  constituted  a  harmonizing 
element  at  all  times  in  the  evolution.  As  the  knots  grew 
up  in  the  midst  of  this  satellitesimal  system,  and  in  this 
orbital  ultra-atmosphere,  and  were  fed  from  them  and 
fed  into  them,  their  nearly  complete  mutual  adjustment 
follows  as  a  natural  consequence.  One  feature  of  this 
adjustment  was  an  evolution  of  the  satellite  orbits  in  the 
direction  of  progressive  circularity  as  in  the  case  of  the 
planetary  family;  so  similarly  there  should  have  been  a 
spacing  of  the  satellite  orbits  into  similar  sub-regularity. 
The  genetic  conditions  made  for  harmony  between  the 


156  THE  ORIGIN  OF  THE  EARTH 

satellites  that  rotated  with  their  primaries,  but  they 
worked  in  a  diversive  way  with  the  recalcitrant  retro- 
grade satellites.  It  is  of  no  little  significance,  in  this  con- 
nection, that  Moulton  foresaw  not  only  that  retrograde 


FIG.  25.— A  double  spiral  nebula,  N.G.C.  4567  and  4568.    Photo- 
graphed at  the  Mount  Wilson  Solar  Observatory. 

satellites  might  arise  under  the  planetesimal  hypothe- 
sis, but  that  their  orbits  would  be  more  eccentric, 
and  their  orbital  planes  more  divergent,  than  those  of 
the  concurrent  satellites.  This  forecast,  based  on  the 


EVOLUTION  OF  THE  PLANETARY  SYSTEM      157 

natural  workings  of  the  mechanics  of  the  case,  has 
proved  true  in  all  the  three  cases  of  recalcitrant  satel- 
lites since  discovered. 


PLANETARY  ATMOSPHERES 

From  the  beginning  of  the  evolution  of  the  planetary 
knots,  theory  indicates  that  there  should  have  been 
an  exchange  between  the  orbital  portion — the  satellitesi- 
mals — that  occupied  the  outer  field  of  the  sphere  of  con- 
trol, and  the  denser  inner  parts  that  formed  the  more 
intimately  organized  collecting  center;  later,  in  the  case 
of  the  earth  and  all  larger  planets,  as  the  evolution  per- 
fected itself,  this  central  mass  gathered  about  itself  a 
threefold  atmosphere,  a  lower  and  denser  collisional 
atmosphere,  graduating  outward  into  a  vaulting  or  krenal 
atmosphere,  and  this,  in  turn,  graduating  into  an 
orbital  atmosphere,  as  set  forth  in  the  first  chapter. 
This  imposed  a  circulatory  influence  upon  the  whole 
assemblage  within  the  sphere  of  control,  except  such 
parts  as,  from  the  beginning,  were  given  an  opposite 
regime  and  were  able  to  retain  a  recalcitrant  attitude. 
The  main  growth  under  these  conditions  tended  toward 
circularity  and  symmetry. 

Thus  the  planetary  system  and,  in  the  main,  the 
satellite  system,  grew  more  and  more  symmetrical  and 
harmonious  as  the  evolution  of  the  spiral  nebula  went 
on.  and  so  came,  in  time,  to  constitute  a  sub-circular 
disk  of  planets,  themselves  the  centers  of  similar  disks 
of  satellites,  in  which,  however,  there  remained 
diversities  of  masses,  of  rotations,  of  inclinations,  of 
eccentricities,  of  space  relations,  and  of  other  features, 


158  THE  ORIGIN  OF  THE  EARTH 

that,  as  dynamic  vestiges,  still  betray  significant  indi- 
vidualities of  origin. 

GENERAL  REFERENCES 

1.  Report  of  T.  C.  Chamberlin,  Carnegie  Institution  of  Washington, 
Year  Book  No.  3  (1904),  pp.  217-33. 

2.  Chamberlin  and  Salisbury',  Geology  (1005),  II,  pp.  60-80. 

3.  F.  R.  Moulton,  Introduction  to  Astronomy  (1906),  pp.  463-87. 


CHAPTER  VIII 
THE  JUVENILE  SHAPING  OF  THE  EARTH 

"As  the  twig  is  bent  the  tree  is  inclined." 
The  juvenile  shaping  of  the  earth  may  be  said  to  have 
begun  as  soon  as  planetesimals  commenced  to  plunge 
into  the  earth-knot  of  the  nebula,  and  both  knot  and 
planetesimals  began  to  gather  into  a  dense  body.  The 
drawing  of  an  atmosphere  close  about  the  young  earth 
commenced  almost  simultaneously.  The  gathering  of 
the  primitive  waters  into  the  hollows  of  the  earth-surface 
soon  followed.  These  three  concurrent  activities  were 
master-processes  in  the  growth  of  the  infantile  earth; 
they  were  the  geologic  triumvirate.  They  wrought 
together  toward  the  earth's  final  shaping  into  the  litho- 
sphere,  the  hydrosphere,  and  the  atmosphere.  Starting 
almost  at  the  beginning  of  the  "earth's  history,  these 
three  great  activities  gave  direction  to  the  planet's 
growth  and  thus  dominated  its  later  career.  Our  in- 
terest now  centers  in  the  way  in  which  the  young  earth 
was  forced  to  depart  from  an  ideal  spheroidal  form  and 
to  take  on  deformative  lineaments  that  grew  at  length 
into  its  present  configurations. 

As  our  genetic  assumptions  are  now  well  understood,  I 
beg  to  indulge  more  freely  in  the  simple  style  of  direct 
affirmation,  when  no  new  assumptions  are  involved. 

SELECTIVE   SEGREGATION   OF  HEAVY  MATERIAL 

As  soon  as  the  more  refractory  substances  of  the 
parent  nebula  began  to  gather  to  one  another  to  form 

159 


160  THE  ORIGIN  OF  THE  EARTH 

minute  aggregates,  these  must  have  taken  on  different 
degrees  of  elasticity  according  to  their  several  natures. 
As  the  collecting  process  involved  collisions,  the  rebounds 
from  the  encounters  became  a  selective  agency,  for  the 
sharp  recoils  of  the  highly  elastic  aggregates  were  less 
favorable  to  concentration  than  the  deadened  responses 
of  the  inelastic  aggregates.  In  these,  the  opposing 
components  of  motion  were  largely  killed  by  collision, 
and,  thus  partially  arrested,  the  aggregates  responded 
more  readily  to  gravity  and  were  more  largely  drawn  to 
the  nucleus.  Inelastic  matter  thus  took  precedence  in 
assembling.  Probably  the  metals — or  their  alloys, 
oxides,  sulphides,  and  similar  compounds — and  the 
basic  silicates  were  leaders  in  this  early  segregation. 
Obviously,  however,  no  such  selective  process  would 
be  complete.  At  most,  it  led  merely  to  a  preponderance 
of  basic  and  metallic  material  in  the  heart  of  the  earth. 

It  is  a  growing  belief  that  all  great  rotating  bodies  are 
magnetic  because  of "  the  electric  charges  they  bear. 
The  magnetism  of  the  sun,  so  brilliantly  demonstrated 
by  Hale  and  his  colleagues,  lends  plausibility  to  this 
view,  for  the  sun  is  too  hot  to  retain  the  familiar  mag- 
netism of  iron  and  its  kindred  metals.  We  have  inferred 
that  the  nebulous  matter  of  the  terrestrial  knot  was 
rotatory  from  its  very  ejection  from  the  sun.  That  it 
should  have  been  affected  by  electric  dissociation  almost 
goes  without  saying.  The  luminosity  of  nebulae  perhaps 
springs  from  their  electric  states.  It  is  then  a  plausible 
conclusion  that  the  earth-to-be  was  magnetic  when  it 
was  only  a  nebulous  knot.  At  any  rate,  the  earth  is  now 
magnetic  and  we  only  follow  the  probabilities  in  pro- 
jecting its  present  qualities  back  to  its  infantile  states. 


THE  JUVENILE  SHAPING  OF  THE  EARTH   161 

If  magnetic,  all  planetesimal  matter  susceptible  to 
magnetic  attraction  would  have  been  drawn  toward 
the  earth-center  by  two  forces,  the  magnetic  and  the 
gravitative.  Iron,  nickel,  cobalt,  and  some  of  their 
compounds  should  have  thus  taken  precedence  over  non- 
magnetic substances  in  entering  the  core  of  the  earth. 
Thus,  the  selective  functions  of  elasticity  and  magnet- 
ism were  perhaps  united  in  concentrating  a  preponderance 
of  heavy  material  in  the  heart  of  the  earth.  Never- 
theless, this  heavy  material  must  have  been  much  mixed 
with  almost  every  other  kind  of  material  and  the  nucleus 
must  have  been  heterogeneous.  It  should  thus  have 
furnished  the  basis  for  a  profound  inner  reorganization; 
this  will  be  the  subject  of  the  next  chapter. 

TEMPERATURE  AND  PHYSICAL  STATE  OF  THE  INTERIOR 

What  temperature  and  what  physical  state  would  have 
arisen  in  the  heart  of  the  earth  from  a  slow  planetesimal 
growth  is  a  question  of  deep  interest,  but  the  final  word 
is  yet  to  be  spoken.  Much  must  have  depended  upon 
the  extent  to  which  orbital  dynamics  prevailed  in  the 
terrestrial  knot.  In  deliberating  on  this  question,  it 
cannot  be  too  constantly  borne  in  mind  that  all  but  a 
small  fraction  of  the  earth-knot  must  have  been  com- 
posed of  matter  that  condenses  to  the  liquid  or  solid 
form  at  high  temperatures.  Even  if  this  dominant 
refractory  matter  escaped  cooling  to  the  solid  state  as  a 
result  of  the  enormous  expansion  it  suffered  on  emerging 
from  the  sun,  it  is  doubtful  whether,  in  so  diffuse  a  state, 
it  could  have  been  maintained  at  vapor  temperatures 
for  any  appreciable  time  after  it  began  to  sweep  through 
interstellar  space.  The  knots  of  spiral  nebulae  are 


1 62  THE  ORIGIN  OF  THE  EARTH 

apparently  quite  persistent,  else  they  would  be  less  com- 
mon. If  only  sustained  by  inter-collisions  of  the  gaseous 
type,  they  might  be  expected  to  collapse  into  a  con- 
centrated form  in  relatively  short  periods.  It  seems, 
therefore,  a  plausible  inference  that  the  orbital  state 
prevailed  in  the  outer  portions  of  the  knots.  The 
interiors  of  the  knots  might  still  be  gaseous. 

Thus  it  appears  that  we  cannot  reason  very  securely 
relative  to  the  primitive  temperatures  of  the  deep  interior 
of  the  embryonic  earth.  It  does  not  seem  imperative 
to  assume  that  the  central  temperatures  were  extremely 
high,  whatever  one  may  think  of  the  probabilities  of  the 
case.  It  does  not  appear  wholly  safe  to  assume  that 
even  the  innermost  core  of  the  earth  took  on  the  liquid 
state,  even  at  the  outset,  or,  if  it  did,  that  it  long  retained 
that  state,  however  congenial  to  inherited  predilections 
such  an  inference  may  be. 

The  conditions  that  controlled  the  accessions  which 
constituted  the  later  growth  of  the  earth  may  be  inferred 
with  more  confidence. 

The  vaporous  nucleus  that  would  directly  condense 
may  have  been  only  a  minor  part  of  the  knot;  the 
primitive  core  may  thus  have  been  small.  Yet  it  would 
be  the  mass  of  the  whole  knot  that  would  be  the  selective 
agency  in  holding  or  failing  to  hold  the  several  grades 
of  molecules.  If  the  mass  of  the  knot  bore  any  such 
ratio  as  we  have  supposed  to  the  mass  of  the  adult  earth, 
it  is  safe  to  assign  it  gravitative  power  enough  to  have 
held  free  nitrogen,  oxygen,  carbon  dioxide,  and  water- 
vapor.  Let  us  proceed,  then,  on  the  assumption  that 
planetesimals  could  reach  the  core  of  the  earth  only  by 
plunging  through  an  envelope  of  satellitesimals  and 


THE  JUVENILE  SHAPING  OF  THE  EARTH      163 

atmosphere.  At  least,  if  an  atmosphere  were  not 
present  at  the  start,  it  would  begin  to  gather  at  an  early 
stage. 

By  far  the  greater  number  of  the  multitude  of  meteor- 
ites that  plunge  daily  into  our  atmosphere  become  white- 
hot  and  are  dissipated  while  yet  in  the  very  thin  upper 
air.  Only  a  very  small  proportion  ever  reach  the  denser 
air  even;  only  rarely,  relatively,  do  meteorites  have  mass 
enough  to  reach  the  earth  before  they  are  completely 
dissipated.  Meteorites  have,  therefore,  almost  no 
power  of  heating  the  body  of  the  earth.  There  is  little 
reason,  then,  to  suppose  that  planetesimals,  even  if 
they  plunged  through  the  satellitesimals  and  into  the 
young  atmosphere  much  more  frequently  than  meteorites 
now  do,  could  have  greatly  heated  the  earth.  It  is  not 
likely  that  the  planetesimals  reached  masses  comparable 
to  such  of  the  meteorites  as  endure  the  atmospheric 
wastage  and  reach  the  earth's  surface.  If  quite  small,  as 
seems  probable  from  the  mode  of  their  formation,  the 
planetesimals  would  be  almost  universally  dissipated  in 
the  upper  air,  even  though  the  young  atmosphere  was 
as  thin  as  that  of  Mars.  Even  if  this  were  not  so,  they 
would  probably  have  been  very  cold  when  they  entered 
the  outer  air  and  might  have  retained  a  cold  interior, 
as  meteorites  sometimes  do,  notwithstanding  the  heating 
of  their  surfaces  by  atmospheric  friction.  Meteorites, 
even  after  they  have  plunged  through  the  whole  atmos- 
phere and  into  the  earth,  are  said  sometimes  to  retain  a 
very  low  temperature  within.  They  are  reported  even  to 
freeze  the  earth  in  which  they  imbed  themselves.  At 
any  rate,  the  low  temperatures  brought  in  from  space 
must  be  set  over  against  the  heat  of  atmospheric  friction 


1 64  THE  ORIGIN  OF  THE  EARTH 

in  the  ledger  of  temperature  effects.  Very  significant, 
in  this  respect,  is  the  almost  incredible  existence  of  a  small 
class  of  meteorites  largely  formed  of  volatile  and  com- 
bustible hydrocarbons.  These  have  reached  the  earth 
without  either  complete  vaporization  or  combustion. 
Meteorites  (which  are,  in  origin  and  in  dynamic  state, 
different  from  planetesimals,  though  the  two  are  not 
uncommonly  confounded)  plunge  into  the  atmosphere  at 
velocities  higher  than  those  which  probably  actuated  the 
planetesimals,  for  the  latter  moved  with  the  earth  and 
their  mean  differences  of  velocity  were  notably  less. 
They  should  have  joined  it  at  perhaps  a  third  or  a  fourth 
of  the  mean  velocity  of  meteorites.  The  conclusion  may 
therefore  be  drawn  rather  firmly  that  very  little  of  the 
heat  of  impact  of  the  planetesimals  affected  the  interior 
of  the  earth's  body. 

The  strokes  of  the  planetesimals  doubtless  gave  rise 
mainly  to  planetesimal  dust  in  the  thin  air  high  above 
the  earth's  surface  where  such  heat  of  impact  as  arose 
was  readily  dissipated.  Settling  thence  gradually  from 
the  outer  air  as  it  did,  there  is  perhaps  as  much  reason 
to  regard  the  planetesimal  dust  as  a  bearer  of  low 
temperature  as  of  high  temperature. 

Leaving,  then,  as  an  open  question  the  temperature 
of  the  innermost  core  of  the  earth — and  so  the  question 
of  its  original  state  of  fluidity  or  solidity — the  matter 
added  in  the  later  stages  by  the  fall  of  planetesimal 
dust  and  planetesimal  residuals  probably  brought  little 
accession  of  heat.  The  weight  which  was  added  by  the 
accessions  of  course  generated  heat  in  the  interior 
by  compression,  but  the  liquefying  effects  of  this  were 
antagonized  by  the  increase  of  pressure  that  caused  it. 


THE  JUVENILE  SHAPING  OF  THE  EARTH      165 

A  like  remark  may  be  made,  with  even  less  reserve,  for 
the  satellitesimal  matter  of  the  knot  when  encountered 
and  carried  down  by  the  plane tesimals. 

From  near  its  beginning,  therefore,  the  earth  is 
pictured  as  growing  up  largely  by  the  accession  of 
planetesimal  dust  after  it  had  been  wafted  to  and  fro  by 
the  atmosphere.  The  accessions  were  solid  matter.  It 
is  our  view  that  they  remained  solid,  except  as  specific 
conditions  enforcing  liquefaction  arose  after  their  burial 
and  reduced  selected  portions  to  the  molten  state. 


fie 

7 


SOURCES   OF   THE   ATMOSPHERE 

The  growth  of  the  atmosphere  of  the  young  earth  is 
assigned  to  three  sources.  A  certain  proportion  of 
nitrogen,  oxygen,  and  other  atmospheric  elements 
doubtless  found  a  place  hi  the  nebulous  knot  at  the 
outset.  In  part  these  elements  were  entrapped  or  com- 
bined with  less  volatile  matter  and  were  carried  with  it 
into  the  growing  earth-body.  Set  free  later  by  internal 
reactions,  a  portion  of  this  atmospheric  material  was 
carried  out  by  volcanic  and  other  extrusive  processes. 
Another  portion  of  the  atmospheric  material  of  the  knot 
probably  escaped  combination  and  entrapment  and 
simply  gathered  more  and  more  closely  about  the  earth- 
body  as  it  grew ;  this  portion  was  merely  the  irreducible 
gaseous  residuum  of  the  knot.  A  third  portion  of  the 
atmosphere  probably  came  in  with  the  planetesimals,  or 
as  planetesimals.  Some  of  this  alien  portion  may  have 
been  in  a  free  molecular  state  as  it  came  in,  that  is,  con- 
stituted molecular  planetesimals;  more  largely  perhaps 
it  had  been  combined,  absorbed,  or  occluded  in  the 
planetesimals  as  they  formed  in  space.  Such  absorbed, 


1 66  THE  ORIGIN  OF  THE  EARTH 

occluded,  or  combined  constituents  were  doubtless 
largely  driven  out  when  the  planetesimals  were  heated 
by  their  plunge  into  the  upper  air;  for  the  rest, 
they  were  probably  given  forth  after  burial  by  internal 
processes.  These  sources  of  gain  imply  that  there 
were  means  of  loss  when  the  nature  of  the  action  was 
reversed. 

The  atmosphere  is  hence  regarded  as  the  product  of  a 
long  and  complex  growth,  beginning  early  and  con- 
tinuing even  to  the  present  day.  This  long  growth 
was  conditioned,  on  the  one  side,  by  the  rate  of  accession 
and  by  the  nature  of  the  added  constituents,  and,  on 
the  other,  by  the  power  of  the  young  earth  to  hold  the 
various  kinds  of  atmospheric  molecules  that  came  to  it, 
as  also  by  the  various  rates  of  their  combinations  with 
earth-substance.  The  conditions  that  affect  the  power 
of  the  earth  to  hold  an  atmosphere  were  discussed  in  the 
first  chapter.  These  conditions  no  doubt  played  a  very 
important  role  in  determining  the  ingredients  and  volume 
of  the  juvenile  atmosphere.  They  have  probably 
served  an  equally  important  function  in  their  selective 
influence  on  the  maintenance  of  the  atmosphere  during 
all  the  ages  that  have  intervened  since. 

It  is  barely  possible  that  the  earth-nucleus,  in  its 
very  earliest  stages,  did  not  have  gravitative  power 
enough  to  hold  an  atmosphere  of  such  active  constituents 
as  free  nitrogen,  oxygen,  and  the  vapor  of  water;  it  is 
barely  possible  also  that  these  elements  were  all  united 
with  the  matter  of  the  knot;  in  either  of  these  cases  the 
primitive  atmosphere  was  probably  formed  only  of 
vapors  whose  molecular  velocities  were  lower,  and  the 
later  atmosphere  must  have  come  almost  wholly  from 


THE  JUVENILE  SHAPING  OF  THE  EARTH      167 

chemical  dissociation  and  from  the  planetesimals  and 
satellitesimals.  But  this  seems,  on  the  whole,  improb- 
able. 

COLLECTION   OF   THE  HYDROSPHERE 

The  gathering  of  the  waters  upon  the  face  of  the  earth 
is  supposed  to  have  been  somewhat  delayed,  at  first,  but 
yet  to  have  soon  joined  the  atmosphere  in  blanketing  the 
globe.  Molecules  of  water- vapor  have  somewhat  higher 
molecular  velocities  than  molecules  of  nitrogen,  oxygen, 
or  carbon  dioxide,  and  hence  an  ocean  may  not  well 
precede  an  atmosphere  in  a  gradual  process  of  growth. 
In  any  case,  water- vapor  should  have  preceded  the 
liquid  form.  If  the  mass  of  the  terrestrial  knot  were  so 
great  as  30  or  40  per  cent  of  the  grown  earth,  it  should 
have  had  gravitative  power  enough  to  hold  water-vapor, 
and,  judging  from  the  chemical  constitution  of  the  sun, 
a  sufficiency  of  appropriate  material  should  have  been 
shot  forth  with  the  knot  to  form  a  hydrosphere  as  well  as 
an  atmosphere  about  as  soon  as  the  mode  of  aggregation 
permitted. 

The  special  property  of  water  responsible  for  the 
growth  of  great  oceans  is  the  persistency  with  which  its 
vapor  condenses  to  the  liquid  form  at  the  temperatures 
that  prevail  at  the  surface  of  the  earth.  Free  nitrogen, 
free  oxygen,  and  most  of  the  other  permanent  constit- 
uents of  the  atmosphere  never  take  the  liquid  form 
under  natural  conditions  of  temperature  and  pressure. 
By  virtue  of  its  prompt  condensation,  water  becomes  a 
very  unstable  constituent  of  the  atmosphere  and  rarely 
forms  any  great  proportion  of  it.  The  liquid  state  is 
water's  normal  form  under  most  terrestrial  conditions. 
None  the  less,  water-vapor  was  doubtless  the  parental 


1 68  THE  ORIGIN  OF  THE  EARTH 

form  of  the  whole  hydrosphere.  If  water-substance  were 
to  be  gradually  removed  from  the  earth,  water-gas  would 
linger  after  liquid  water  had  disappeared ;  so,  by  reversal, 
it  quite  certainly  appeared  before  water  condensed. 
At  all  times  after  their  inception,  the  water- vapor  envel- 
oping the  earth  and  the  waters  on  its  surface,  strove  to 
maintain  an  equilibrium  between  themselves,  but  this 
was  greatly  embarrassed  by  constant  changes  of  tem- 
perature, and  was  furthermore  much  interrupted  and 
restrained  by  the  circulation  of  the  atmosphere,  and  so 
the  juvenile  earth  undoubtedly  had  its  arid  regions 
as  well  as  its  humid  regions.  The  old  picture  of  a 
warm  moist  atmosphere  enveloping  the  whole  earth 
is  held  to  be  physically  untenable  even  under  the 
conditions  of  the  early  geologic  ages,  for  descending 
air  currents  in  a  natural  circulation  are  inevitably  dry 
currents. 

CO-OPERATION     OF     LITHOSPHERE,     HYDROSPHERE,     AND 
ATMOSPHERE 

Our  general  picture  of  the  history  of  the  juvenile 
planet  is  then  tripartite,  a  small  lithosphere,  a  small 
atmosphere,  and  a  small  hydrosphere  growing  up 
together  in  co-operation  and  at  the  same  time  in  com- 
petition and  antagonism,  and  so,  by  their  interactions, 
working  out  their  adjustments  to  one  another  pro- 
gressively. The  environing  conditions  are  not  regarded 
as  radically  different  from  those  of  the  geologic  ages,  or 
of  the  present.  Notable  oscillations,  however,  ran 
through  the  whole  history.  The  picture  is  quite  at 
variance  with  the  traditional  one  sketched  in  the 
Introduction. 


THE  JUVENILE  SHAPING  OF  THE  EARTH      169 

The  story  of  the  interactions,  the  competitive 
struggles,  and  the  mutual  adjustments  of  the  great 
triumvirate  in  progressively  shaping  the  lithosphere,  the 
hydrosphere,  and  the  atmosphere  throughout  the  ages 
is  the  task  assumed  by  geology.  The  great  contest, 
however,  had  its  origin  in  the  genesis  of  the  earth,  and  the 
main  lines  of  the  contest  took  form  in  the  earth's  infan- 
tile ages.  We  should  fail  to  tell  a  vital  part  of  the 
story  of  the  earth's  beginning  if  we  passed  without  note 
the  inception  and  the  early  alignment  of  the  prolonged 
struggle  that  is  the  very  soul  of  geologic  history. 

At  the  stage  when  first  the  stratigraphic  record 
becomes  distinctly  legible,  the  struggle  of  earth,  air,  and 
water  had  attained  working  relations  much  the  same  as 
they  bear  today.  The  lithosphere  had  taken  on  great 
continental  reliefs  and  great  oceanic  depressions.  Then, 
as  now,  apparently  about  two-thirds  of  the  surface  was 
deeply  submerged  and  about  one-third  was  strongly 
bowed  upward.  The  waters  sometimes  confined  them- 
selves to  the  abysmal  depressions  and  sometimes  flooded 
the  lower  borders  of  the  continental  protrusions.  The 
waters  and  the  air  joined  forces  in  a  ceaseless  endeavor 
to  wear  down  the  protrusions,  but  they  rarely  more 
than  half  succeeded  before  the  accumulated  stresses  of 
the  lithosphere  brought  on  a  new  series  of  deformative 
readjustments  by  which  the  continental  protrusions  were 
renewed,  the  basins  deepened,  and  the  waters  with- 
drawn more  largely  into  the  abysmal  depths.  The 
powers  of  the  lithosphere,  though  only  now  and  then 
made  manifest  in  marked  degree,  have  thus  far  held 
the  mastery.  The  final  issue  hangs  no  doubt  on  the 
hidden  resources  of  renewable  reshaping  power  in  the 


170  THE  ORIGIN  OF  THE  EARTH 

lithosphere.  If  these  resources  shall  fail,  the  unceasing 
gnawings  of  the  rains,  the  winds,  the  streams,  and  the 
seas  will  certainly  cut  away  the  land  and  leave  a  uni- 
versal ocean,  save  as  volcanic  piles — if  the  volcanoes  still 
live — may  rise  above  its  surface.  If  the  hidden  powers 
of  the  lithosphere  shall  seriously  weaken  with  time, 
the  periodic  incursions  of  the  sea  will  disastrously  con- 
strict land  life  at  the  epochs  of  crisis.  But  if  the  hidden 
powers  of  the  lithosphere  are  adequate  to  indefinite 
renewal,  continued  rejuvenations  of  the  continents  may 
be  assumed  to  be  assured.  The  ultimate  issue  hangs 
on  the  reserve  power  of  re-formation — we  say  deforma- 
tion— inbred  in  the  lithosphere  in  its  youth.  From  this 
the  renewal  springs.  The  nature  of  these  inbred  re- 
sources is  now  our  problem. 

Let  us  recall  the  processes  of  growth  that  gave  the 
basal  elements  of  this  inbred  power,  as  interpreted  by 
the  planetesimal  hypothesis.  The  earth-body  grew 
up  by  a  multitude  of  minute  accessions  coming  by  way 
of  the  atmosphere  and  carried  by  it  to  resting-places 
far  or  near  as  conditions  determined.  The  atmosphere 
thus  took  the  first  turn  at  the  distribution  of  the  earth's 
new  material.  If  the  accessions  fell  into  the  waters, 
these  took  the  next  turn  and  bore  the  accessions  along 
their  courses  to  resting-places  which  they  determined. 
The  lithosphere  was  permitted  to  receive  its  accretions 
only  as  dictated  by  these  intermediary  agencies. 

But,  on  the  other  hand,  the  configuration  of  the  earth- 
body  had  previously  determined  where  the  waters  should 
lie,  and,  in  some  measure,  how  they  should  move,  and 
had  thus  circumscribed,  by  its  own  prior  action,  the 
water's  control  over  the  accessions.  In  a  less  obvious 


THE  JUVENILE  SHAPING  OF  THE  EARTH      171 

way,  the  configuration  of  the  earth's  surface  had  given 
shape  and  place,  in  some  degree,  to  the  great  swirls  and 
gyrals  of  the  atmosphere,  and,  to  that  extent,  pre- 
scribed the  control  of  the  first  controller  of  the  planetesi- 
mal  dust.  Here  is  a  tangle  of  contesting  agencies  most 
forbidding  to  the  inquirer  who  would  read  their  history 
in  their  results. 

The  task  is  further  embarrassed  by  interchanges  of 
cause  and  effect.  Each  cause  is  no  sooner  realized  in 
an  effect  than  this  effect  becomes  a  new  cause,  and  so  the 
chain  of  sequence  runs  indefinitely  on.  Not  only  this, 
but  an  atmospheric  cause  gives  a  result  in  terms  of 
hydrospheric  or  lithospheric  phenomena,  and  this  result, 
becoming  at  once  a  cause,  may  either  yield  a  result  in  its 
own  field  or  in  the  field  of  either  one  of  the  others.  Thus 
there  arises  an  intricate  intertanglement  of  antecedents 
and  consequents  that  are  in  a  sense  interchangeable. 

To  trace  back  to  their  initial  stages  the  contribution 
of  each  agency  is  scarcely  less  than  a  hopeless  task. 
To  start  with  a  hypothetical  cosmogonic  status  and 
trace  forward  the  special  modes  of  action  and  the  values 
of  participation  of  each  of  the  three  great  factors,  deduc- 
tively, is  scarcely  more  hopeful.  To  try  to  do  both  and 
to  shape  each  to  fit  the  other  may  seem  to  savor  of 
selective  adjustment  and  mutual  accommodation,  but 
it  is  legitimate  if  used  merely  as  a  means  of  guiding 
deduction  by  observed  consequences,  and  of  guiding 
induction  by  discernible  antecedents.  The  mutual  sug- 
gestiveness  of  such  a  reciprocal  method  gives  it  the 
meager  promise  which  alone  the  entangled  case  affords. 
It  will  no  doubt  take  years  of  persistent  trials  to  work 
out  the  full  chain  of  causes  and  effects  that  led  to  the 


172  THE  ORIGIN  OF  THE  EARTH 

results  revealed  in  the  adult  earth.  But  the  longer 
the  road,  the  sooner  a  start  were  best  made,  however 
falteringly. 

SHAPING  AGENCIES 

The  lord  of  the  shaping  agencies  was  obviously  gravi- 
tation, whose  ideal  product  is  a  perfect  sphere,  the 
standard  from  which  deformations  are  measured.  By 
far  the  most  powerful  of  the  deforming  agencies  was 
rotation.  In  the  course  of  the  earth's  past  history  it  has 
imposed  on  the  ideal  earth-sphere  dictated  by  gravita- 
tion a  series  of  depressions  of  the  high  latitudes — inter- 
rupted probably  with  many  intervening  elevations — and 
a  series  of  swells  of  all  the  low  latitudes — interrupted 
probably  with  many  intervening  depressions — the  whole 
series  resulting  in  a  graduated  polar  flattening  and  a 
graduated  equatorial  bulge,  technically  a  zonal  harmonic 
deformation  of  the  second  order.  The  residual  values  of 
all  these  past  deformations  now  appear  as  differences  in 
the  earth's  radii  ranging  up  to  13.4  miles  (21.6  kilo- 
meters). The  deformations  that  most  nearly  rival  this 
in  magnitude  are  the  continental  swells  and  oceanic  sags. 
The  vertical  swing  of  these  is  less  than  half  that  of 
the  rotational  effect,  while  the  amplitude  is  also  very 
much  smaller.  Even  the  utmost  range  of  mere  detail 
measured  from  the  highest  mountain  peak  to  the  lowest 
known  sea-deep,  falls  short  of  the  broad  rotational  range, 
while  the  masses  involved  in  the  peaks  and  deeps  are 
trivial  compared  with  those  of  the  harmonic  rotational 
deformation. 

In  addition  to  its  marked  superiority  in  potency, 
rotation  quite  surely  took  precedence  in  doing  its  deform- 
ative  work;  it  was  an  active  force  at  the  very  outset; 


THE  JUVENILE  SHAPING  OF  THE  EARTH      173 

very  likely  it  was  more  effective  in  the  growing  stages 
than  afterward.  In  our  picture  of  earth-genesis,  rota- 
tion co-operated  with  gravitation  even  in  giving  the 
core  of  the  earth  its  initial  form.  The  deformative 
work  of  shrinkage  and  similar  agencies  could  only  have 
come  into  effect  later.  The  initial  departures  of  the 
earth  from  an  ideal  sphere  are  therefore  assignable 
chiefly  to  rotation. 

The  simple  harmonic  swell  at  the  equator  and  flatten- 
ing at  the  poles  need  not,  however,  detain  us;  this  is 
not  the  special  point  of  interest,  but  rather  the  secondary 
deformative  effects,  commonly  altogether  neglected. 
These  arise  from  the  adjustments  that  are  forced 
whenever  there  is  any  appreciable  change  in  the  rate  of 
rotation.  It  is  obvious  that  if  the  rate  of  rotation  is 
increased,  the  high  latitude  areas  must  sink,  and  in  so 
doing  suffer  mutual  crowding  and  compression;  while 
the  low  latitudes  must  rise  and  suffer  tension;  and 
vice  versa,  if  the  rotation  is  slackened.  It  is  the  effect 
of  such  changes  on  the  shape  of  the  juvenile  earth  that 
requires  consideration.  There  is  need,  therefore,  first 
to  consider  the  nature  of  the  changes  in  the  rate  of 
rotation  that  probably  arose  in  the  early  history  of  the 
earth,  and  then  to  study  their  deformative  effects  on  the 
globe. 

Let  us  note,  then,  at  the  outset  that  the  present  rota- 
tion of  the  earth  is  only  the  outcome  of  a  long  history; 
the  net  result  may  be  far  from  a  true  index  of  the  sum- 
total  of  rotational  effects  of  all  past  time.  This  total 
value  it  is  impossible  to  estimate  in  more  than  the 
roughest  way,  even  if  the  planetesimal  theory,  in  the 
venturesomely  specific  form  we  have  given  it  for  just 


174  THE  ORIGIN  OF  THE  EARTH 

such  trial  purposes,  be  fully  accepted;  but  a  review  of  the 
assigned  conditions  may  be  helpful  toward  a  tentative 
picture  of  the  case. 

The  initial  rotation  of  the  earth-knot  is  assigned  to  the 
inequalities  of  the  impulse  that  shot  it  from  the  sun  and 
to  the  inequalities  of  resistance  to  its  escape.  Deduc- 
tions from  the  nature  of  the  case,  as  well  as  inferences 
from  the  observed  outlines  of  nebular  knots,  favor  an 
orbital  deployment  of  the  knots  in  some  large  degree 
at  least,  and  this  implies  much  rotatory  momentum  at 
the  start. 

But  the  critical  element  probably  lay  in  the  effect  later 
produced  by  the  infall  of  planetesimals  as  they  gradually 
built  up  the  earth  nucleus  into  the  adult  planet.  Near 
the  close  of  the  fifth  chapter,  attention  was  called  to 
the  reasons  for  believing  that  the  effects  of  the  infalling 
matter  tended  toward  an  equilibrium  value.  This  effect 
should  have  tended  to  reduce  any  inherited  rotation 
to  the  equilibrium  value  and  to  maintain  an  equilibrium 
rate  of  rotation  based  on  that  value.  It  was  pointed 
out  that  the  mechanism  would  tend  to  keep  the  rate  of 
rotation  oscillating  about  this  equilibrium  value.  The 
planetesimals  were  very  irregularly  dispersed  along 
the  arms  of  the  nebulae,  and  the  knots  were  unsym- 
metrically  placed  relative  to  the  nebular  streams,  so 
that,  in  spite  of  all  smoothing  out  of  effects  by  the 
compensations  of  chance  distribution,  the  net  effects 
must  have  been  inconstant,  and  the  rate  of  rotation 
must  have  oscillated  about  the  equilibrium  rate.  It 
was,  however,  pointed  out  that  the  equilibrium  rate  itself 
was  almost  certain  to  undergo  changes  with  the  altera- 
tion of  basal  conditions  that  arose  from  the  progressive 


THE  JUVENILE  SHAPING  OF  THE  EARTH      175 

ingathering  of  the  plane tesimals.  Thus,  even  after  an 
equilibrium  rate  was  once  reached,  the  whole  history  of 
rotation  should  have  been  one  of  oscillation,  and  oscilla- 
tion should  even  have  marked  the  progress  toward  the 
equilibrium  rate. 

Superposed  on  the  deformative  effects  of  rotation  were 
those  that  sprang  from  the  tides  and  from  the  shrinking 
of  the  earth-body.  The  former  were  doubtless  slight, 
but  the  latter  were  important.  As  the  earth  was  built 
up  by  the  accession  of  finely  divided  matter  laid  down 
by  air  or  water,  and  as  this  loose  material  was  pro- 
gressively buried,  there  inevitably  ensued  much  compres- 
sion and  much  molecular  reorganization  to  secure 
greater  density.  While  the  condensation  was  no  doubt 
progressive,  it  probably  obeyed  the  higher  law  of  pulsa- 
tory action  and  fell  into  the  periodic  habit  that  so  notably 
marked  the  well-known  stratigraphic  ages.  In  any  case, 
the  shrinkage  tended  to  accelerate  the  rate  of  rotation; 
if  periodic,  the  acceleration  was  periodic.  Episodes  of 
acceleration  from  shrinkage  are  pictured  as  occurring 
at  intervals  all  through  the  growing  stages  of  the  earth 
even  more  frequently  than  in  later  times,  and  they  must 
have  tended  to  raise  the  speed  of  rotation  above  the 
equilibrium  rate  and  incite  a  tendency  to  restoration  in 
which  the  infalls  and  the  tides  would  co-operate. 

It  appears,  therefore,  that  changes  of  rotation  were 
the  order  of  the  day  during  the  growth  of  the  juvenile 
earth.  In  the  known  geologic  ages,  the  effects  of  growth 
are  negligible,  but  there  continues  to  this  day  a  contest 
between  tidal  retardation  and  its  allies,  on  the  one 
hand,  and  shrinkage  acceleration  and  its  allies,  on  the 
other. 


1 76  THE  ORIGIN  OF  THE  EARTH 

From  recent  exact  studies  of  the  moon  by  Brown1 
and  others,2  *nd  3  and  from  comparisons  of  the  moon's 
irregularities  with  those  of  Mercury  and  Venus, 
there  appears  to  be  some  ground  to  suspect  that 
even  now  there  are  changes  in  the  earth's  rotation 
that  may  be  astronomically  detected.  In  view  of 
the  shortness  of  the  observational  periods  avail- 
able, this  is  more  than  could  confidently  have  been 
expected,  but  if  it  shall  be  realized,  it  may  be  re- 
garded as  quite  in  harmony  with  genetic  and  geologic 
antecedents. 

If  the  rate  of  rotation  has  changed  often,  the  vital 
question  arises:  How  did  the  earth  accommodate  itself 
to  the  compressional  and  tensional  stresses  that  inevit- 
ably accompanied  the  reciprocal  swellings  and  sinkings 
of  polar  and  equatorial  regions  ?  Obviously  this  would 
depend,  so  far  as  its  precise  manner  is  concerned,  on 
the  physical  state  of  the  interior.  Consistently  with 
what  has  been  said  before,  and  conformably  with  the 
virtual  demonstrations  of  the  solid  state  of  the  interior, 
our  discussion  will  proceed  on  the  assumption  that  the 
earth,  at  all  stages  of  final  shaping,  was  an  elastic  solid 
of  high  rigidity.  We  shall  pass  lightly  all  consideration 
of  the  innermost  core  of  the  earth  on  which  a  final 
opinion  may  wisely  be  held  in  abeyance.  We  shall, 
however,  class  it,  by  implication,  with  the  rest,  for  unless 
there  are  cogent  reasons  for  assigning  it  a  different  state, 
the  most  conservative  view,  pending  further  seismic 
data,  is  to  assume  that  it  followed  the  habit  of  the  main 
body  of  the  earth.  The  mechanism  of  extrusion,  which 
we  shall  later  discuss,  would  probably  force  a  solid  con- 
dition upon  it,  whatever  its  original  state.  The  recent 


THE  JUVENILE  SHAPING  OF  THE  EARTH      177 

tidal  determinations  of  Michelson4  and  colleagues5  seem 
to  imply  such  a  state. 

DISTRIBUTION  OF  STRESSES 

The  dynamic  basis  for  deduction  is  a  vital  feature. 
It  cannot  be  too  thoughtfully  considered  that  the  stress- 
differences  generated  by  changes  in  the  earth's  rate  of 
rotation,  according  to  Sir  George  Darwin,6  not  only 
pervade  the  whole  interior,  but  increase  progressively 
from  surface  to  center  where  they  are  eight  times  as 
great  as  at  the  surface.  There  is  a  curious  variation 
from  a  simple  gradation  of  stress-difference  from  the 
center  to  the  surface  in  the  sub-polar  portion,  as  shown 
in  the  accompanying  diagram  (Fig.  26)  reproduced  from 
Darwin's  classical  discussion,  but  that  may  be  neglected 
here.6  The  internal  stress-differences  of  the  tides  have 
the  same  distribution,  according  to  the  same  high 
authority.  So  does  any  weighting  or  relief  of  load  that 
takes  the  form  of  a  belt  about  any  equator  of  the  globe 
with  polar  areas  of  the  opposite  state. 

If  resistance  to  movement  under  rotational  stress 
were  equal  at  all  depths — or  were  easiest  in  the  central 
parts,  by  reason  of  a  mobile  state — adjustment  move- 
ments in  the  central  parts  would,  we  infer,  take  prece- 
dence, because  the  stress-differences  are  there  greatest. 
Equal  facility  of  movement  would  obtain  when  the  resist- 
ances were  distributed  according  to  the  same  law  as  the 
stress-differences,  in  this  case  a  gradation  of  resistances 
from  eight  at  the  center  to  one  at  the  surface.  The 
high-pressure  results  of  Adams,7  Bridgman,8  and  others 
show  a  relatively  rapid  increase  of  rigidity  with  increase 
of  pressure.  If  an  extrapolation  of  these  to  the  heart  of 


78 


THE  ORIGIN  OF  THE  EARTH 


the  earth  could  be  trusted,  the  relative  resistances  to 
deformation  there  would  be  much  higher  than  the 
relative  stress-differences  arising  from  change  of  rota- 
tion. But  even  if  there  were  no  doubt  as  to  the  con- 
tinuance of  the  high  rate  of  increase  of  rigidity,  the 
conclusion  would  jxrhaps  only  apply  to  the  average 


PbU 


FIG.  26. — Diagram  showing  curves  of  equal  stress-difference  due  to 
the  weight  of  second  harmonic  inequalities  or  to  tide -generating  force. 
(Darwin.) 

mass;  very  likely  it  might  not  apply  to  special  tracts 
where  cleavage  lines,  schistosity,  and  other  facilities 
for  movement  had  been  developed  previously  by  ease- 
ment movements.  It  is  assumed  that  structural  adjust- 
ments to  movement  adequate  to  meet  the  demands 
of  stress-differences  of  a  high  order  arising  from  rota- 


THE  JUVENILE  SHAPING  OF  THE  EARTH      170 

tion  were  developed  in  each  stratum  soon  after  it  was 
added  at  the  surface,  and  that  these  structural  and 
textural  features  were  retained,  or  were  renewed  as 
new  requirements  demanded  while  they  were  in  process 
of  burial  to  greater  and  greater  depths.  Otherwise 
that  nearly  perfect  adjustment  to  rotational  demands 
which  the  earth  now  exhibits,  and  which,  judging  from 
the  distribution  of  the  waters  in  the  past,  has  prevailed 
throughout  geologic  history,  would  probably  not  have 
been  realized.  This  is  closely  locked  up  with  the  ques- 
tion whether  the  crystalline  structure  developed  near 
the  surface  would  be  retained  as  the  layers  were  pro- 
gressively buried  under  greater  and  greater  weight.  So 
far  as  both  geological  and  experimental  evidence  goes, 
increasing  load  favors  crystallization  in  rock  substances, 
except  in  the  extremely  few  cases  in  which  crystalli- 
zation involves  expansion,  as  in  ice  and  in  bismuth. 
Since  increasing  load  favors  recrystallization  into  a 
denser  form,  there  is  a  strong  presumption  that,  as 
surface  layers  were  more  and  more  deeply  buried, 
there  would  be  a  series  of  recrystallizations  in  the  inter- 
est of  increasing  density.  So  probably  there  would  be 
chemical  recombinations  of  like  import.  All  this  looks 
not  only  toward  continued  but  toward  progressive 
crystallization  with  increasing  depth.  It  seems  inher- 
ently probable  that  such  crystalline  assemblages  of  mole- 
cules of  like  kinds,  or  of  molecules  mutually  suited  to  one 
another,  as  serves  the  interests  of  compactness  and  order 
near  the  surface,  would  continue  to  obtain,  abetted  by 
adaptive  changes,  in  the  depths  of  the  earth.  This  seems 
to  be  in  close  accord  with  the  tenor  of  such  specific 
evidence  as  is  applicable  to  the  case. 


i8o  THE  ORIGIN  OF  THE  EARTH 

INTERNAL  MOVEMENT 

With  little  doubt,  our  best  guide  in  forming  a  picture 
of  the  probable  mode  by  which  adjustment  movements 
were  carried  into  effect  in  the  deep  interior  is  to  be 
found  in  the  method  by  which  the  deepest  accessible 
rocks  have  accomplished  similar  adjustment  movements. 
In  our  view,  the  adjustment  tracts  were  mechanically 
selected  in  each  stratum,  or  group  of  strata,  while  still 
near  the  surface ;  it  was  then  that  deformative  force  was 
first  brought  to  bear  upon  it;  the  resulting  structures 
and  textures  were  slowly  carried  down  to  deeper  horizons 
as  burial  proceeded,  and  only  progressive  changes  are 
to  be  considered.  The  initial  conditions  were  those 
of  ordinary  diastrophism  near  the  surface.  The  only 
special  question  is  whether  the  structures  and  textures 
inherited  from  this  sub-surficial  diastrophism  would 
remain  serviceable  for  movement  as  weight  was  added, 
and  would  remain  susceptible  of  further  structural 
evolution  such  as  would  be  serviceable  for  movement 
under  the  increasing  pressures  and  stress-differences. 
This  is  closely  tied  up  with  the  question  whether  crystal- 
lization can  extend  to  the  depths  of  the  earth,  a  subject 
touched  a  moment  ago.  In  addition  to  the  considera- 
tions there  urged,  it  may  be  added  that  this  question 
receives  a  probable  answer  in  the  transmission  of  the 
distortional  phase  of  earthquake  waves  through  the 
deep  interior,  as  recorded  by  seismic  instruments.  The 
transmission  of  distortional  waves  implies  an  elastic  solid 
condition.  In  the  core  of  the  earth,  the  transmission  of 
distortional  waves  at  accelerated  rates,  through  more 
than  half  the  volume  of  the  earth,  probably  implies 
specifically  the  continuance  of  crystalline  structure  to  a 


THE  JUVENILE  SHAPING  OF  THE  EARTH      181 

like  extent,  at  least,  since  the  crystalline  structure  is  the 
typical  form  of  elastic  earth-substances.  The  few 
exceptional  cases  in  which  "  undercooled  liquids/'  such  as 
obsidian  and  other  glasses,  show  facility  in  transmitting 
distortional  waves  can  hardly  have  any  bearing  on  this 
problem,  since  the  hot  interior  of  the  earth  is  not  a 
suitable  environment  for  "undercooled"  liquids.  For 
depths  that  involve  more  than  half  the  volume  of  the 
earth,  the  speed  of  the  distortional  waves  increases 
notably  with  the  depth,  which  implies  that  elastic 
rigidity  rises  faster  than  density,  for  the  latter  tends  to 
reduce  the  rate  of  transmission.  Toward  the  center  of 
the  earth  a  change  seems  to  take  place  and  the  interpre- 
tation of-  the  seismic  waves  is  embarrassed  by  uncer- 
tainties due  to  imperfect  or  insufficient  data.  Pending 
better  data,  we  prefer  to  ascribe  the  change  in  the  seismic 
waves  to  a  change  of  earth-substance  from  predominant 
silicates  in  the  outer  part  to  predominant  alloys  in  the 
heart  of  the  earth.  The  high  specific  gravity  of  the 
latter  should  damp  the  speed  of  the  waves  and  might 
naturally  induce  troublesome  refractions. 

It  seems,  therefore,  most  in  line  with  the  trend  of  the 
results  of  recent  investigations  to  assume  that  a  crystal- 
line state  extends  far  down  into  the  depths  of  the  earth, 
if  not  to  its  very  center.  So,  also,  it  seems  most  in  the 
line  of  probabilities  to  assume  that  movements  forced 
on  this  crystalline  mass  by  stress-differences  in  the 
deeper  horizons  will  follow  the  methods  that  obtain  in  the 
lowest  horizons  laid  bare  for  study  by  denudation  and 
diastrophism;  or  if  not  by  these  precisely,  by  supple- 
mentary methods  of  like  nature  applicable  to  the  crystal- 
line state. 


1 82  THE  ORIGIN  OF  THE  EARTH 

MODE   OF  INTERNAL  MOVEMENT 

Now  the  chief  mode  by  which  solid  rocks  under  high 
pressure  and  heat  adjust  themselves  to  great  stress- 
differences  is  by  recombination  and  recrystallization,  as 
brought  out  by  recent  investigations  in  the  field  and  in 
the  laboratory.9'14  By  chemical  and  physical  recombina- 
tions and  rearrangements,  the  rock  rhaterial  is  reshaped 
into  crystalline  forms  adapted  to  the  imposed  movement. 
The  change  seems  to  be  effected  by  free  molecules  acting 
individually,  or  in  groups,  only  a  small  portion  of  the 
molecules  undergoing  change  at  any  one  time,  the  rest 
retaining  their  fixed  adhesions,  so  that  the  mass,  as  a 
whole,  remains  essentially  solid  all  the  time,  and  may 
be  quite  rigid  at  all  stages.  In  general,  the  mass  does  not 
seem  to  become  even  viscous.  The  relatively  few 
molecules  that  are  changing  their  adhesions  and  combi- 
nations at  any  instant,  or  are  leaving  one  crystalline 
attachment  and  finding  a  new  one  better  accommodated 
to  the  urgencies  of  the  stress,  seem  to  have,  for  the  time 
being,  a  freedom  of  the  fluidal  type.  Just  how  they 
make  their  way  from  one  point  to  another  among  or 
through  the  crystals  that  form  the  prevailingly  solid 
rock  is  undetermined,  but  the  fact  seems  incontestable. 
The  observed  result  is  the  formation  of  new  crystals,  or 
reshaped  crystals,  in  parallel  adjustment  to  the  lines  of 
movement.  Platy  and  columnar  crystals  are  induced 
so  far  as  the  nature  of  the  material  will  permit,  and  their 
parallel  arrangement  gives  rise  to  cleavage  between  the 
crystals  in  the  direction  of  movement.  This  parallel 
orientation  of  the  crystals  carries  with  it  the  crystal's 
own  internal  cleavage.  The  total  action  is  conveniently 
called  " rock-flow"  or  "solid-flow,"  but  it  is  not  to  be 


THE  JUVENILE  SHAPING  OF  THE  EARTH      183 

confounded  with  liquid  flow  or  viscous  flow .  The  textural 
result  is  a  schistose  tract.  The  plane  of  schistosity  is  in 
general  accord  with  the  direction  of  movement  which  is 
in  the  line  of  least  resistance.  In  the  case  in  hand,  the 
lines  of  least  resistance  are  dominantly  directed  toward 
the  surface,  and  the  schistose  tracts  should  be  vertical. 
This  is  not  in  contravention  of  the  tendency  to  horizontal 
or  low-angle  schistosity  in  certain  surficial  or  sub- 
surficial  situations  where  the  dominant  arrangement 
of  forces  is  different. 

It  is  therefore  assumed,  as  the  safest  tentative  work- 
ing basis,  that  in  whatever  tract  the  stress-differences 
came  to  be  most  intense,  recombination  and  recrystalliza- 
tion  took  place  in  the  yield  zones  by  the  individual  move- 
ments of  freed  molecules,  with  incidental  cleavage  and 
schistosity,  and  that  the  requisite  movements  and  adjust- 
ments were  thereby  accomplished.  It  may  be  noted  that, 
if  this  method  became  inadequate  at  any  time,  or  in  any 
place,  the  parallel  planes  previously  generated  were 
fitted  to  facilitate  forced  movement  of  a  more  intensive 
mechanical  sort. 

It  is  worthy  of  noting  here  that,  if  this  method  of 
stress-easement  is  not  available  in  the  heart  of  the  earth, 
it  does  not  necessarily  vitiate  the  more  essential  features 
of  the  interpretations  that  follow.  However,  no  limits 
to  the  process  of  crystallization  and  recrystallization  are 
known  under  interior  conditions  short  of  melting  and 
mutual  solution.  These  latter  probably  contributed  to 
the  deeper  movements  more  largely  than  to  the  more 
superficial  ones,  but  the  prevalence  of  liquid  material 
seems  to  be  rather  markedly  restricted  by  the  evidences 
of  elastic  rigidity. 


1 84  THE  ORIGIN  OF  THE  EARTH 

Granted  that  this  mode  of  accommodation  was  avail- 
able for  stress-easement  in  the  tracts  where  stresses 
were  concentrated,  the  intervening  masses  were  left 
relatively  free  to  develop  such  higher  degrees  of  rigidity 
as  the  imposed  pressures  might  have  required. 

INTERNAL    MOVEMENTS    REQUIRED    BY    ROTATIONAL 
CHANGES 

The  shifts  of  matter  within  the  earth  required  to 
reshape  it  to  fit  a  new  rotational  rate  are  easily  pictured. 
If  rotation  slackens,  the  equatorial  tract  tends  to  sink 
and  suffer  compression,  while  the  polar  portions  tend  to 
rise  and  suffer  tension.  Between  the  rising  and  falling 
tracts  lie  fulcrum  zones  in  which  there  is  neither  rise  nor 
fall.  Across  each  fulcrum  zone,  however,  there  must  be 
a  shift  of  matter  sufficient  to  relieve  the  sinking  equa- 
torial tract  and  supply  the  rising  polar  tracts.  These 
fulcrum  zones  lie  not  far  from  30°  Lat.  N.  and  S.;  their 
precise  positions  vary  with  the  degree  of  oblateness ;  but 
we  need  not  dwell  on  these  refinements.  If  rotation 
increases,  the  shifts  are  reversed,  with  reversal  of  com- 
pressional  and  tensional  effects. 

If  the  earth  had  a  fluid  interior,  the  main  shifts  would 
be  made  by  flow  in  the  true  sense,  but  compressional  and 
tensional  effects  in  the  crust  would  be  felt  and  the  deduc- 
tions that  follow  would  probably  hold  in  a  modified  form. 
But  if  the  earth  is  solid,  with  increasing  rigidity  toward 
the  center,  as  growing  evidence  seems  to  imply,  the 
shifts  will  tend  to  take  place  by  massive  movements 
that  involve  the  least  possible  strain  throughout  the  body 
and  that  throw  as  much  of  the  deformative  action  as 
possible  on  zones  of  easiest  yield.  The  number  of  lines 


THE  JUVENILE  SHAPING  OF  THE  EARTH      185 

of  deformation  will  tend  toward  a  minimum,  so  far  as 
these  can  ease  the  stress.  It  is  fairly  safe  to  assume 
that  the  simplest  segmentation  of  the  body  of  the  earth 
that  would  accommodate  the  main  stresses  imposed  by 
changes  of  rotation  was  that  most  likely  to  have  been 
adopted.  Minor  and  more  local  stresses  should  have 
been  eased  by  supplementary  lines  restricted  to  the 
lesser  demands. 

PRIMARY    SEGMENTATION    OF    THE    EARTH-BODY 

In  seeking  the  simplest  mode  of  accommodation  to 
rotational  requirements,  it  may  be  first  noted  that,  at 
the  surface  at  least,  where  the  action  probably  started, 
tensional  stresses  are  easier  relieved  by  disruption  than 
compressional.  If  the  rotation  inherited  from  the 
earth-knot  was  greater  than  that  of  the  equilibrium 
rate  imposed  later  by  the  infall  of  planetesimals,  as 
seems  probable,  the  net  tendency  in  the  early  ages 
would  be  toward  slackening  rotations,  and  hence  toward 
compression  in  the  equatorial  belt  and  tension  in  the 
polar  tracts.  It  is  probable,  therefore,  that  segmentation 
began  under  tensional  conditions  near  the  poles — where 
the  stresses  would  be  twice  as  great  as  at  any  given  point 
on  the  equator — and  that  the  other  primary  lines  of 
accommodation  developed  from  these  initial  ones.  A 
like  inference  is  to  be  drawn,  even  if  segmentation 
did  not  start  until  after  the  rate  of  rotation  had  reached 
a  stage  of  oscillation  about  the  equilibrium  value,  for  the 
tensional  stage  would  act  under  less  stress  than  the 
compressional  and  so  would  be  likely  to  precede  it, 
defining  the  lines  of  accommodation.  But  the  order  of 
precedence  is  probably  not  at  all  vital;  it  is,  however, 


1 86  THE  ORIGIN  OF  THE  EARTH 

convenient  to  follow  a  definite  line  of  interpretation, 
and  the  most  probable  line  is  preferable,  even  if  it  is  not 
important. 

Fortunately,  the  earth  gives  very  instructive  illus- 
trations of  how  tensional  stresses  are  relieved.  The  most 
illuminating  example,  especially  for  our  purpose,  is  the 
mode  of  partition  followed  by  certain  basic  lavas  as 
they  solidify,  and  shrink  in  so  doing.  The  result  is  a 
columnar  structure,  well  shown  in  the  basaltic  columns 
of  the  Giant's  Causeway,  FingaPs  Cave,  the  Devil's 
Post  Pile,  and  numerous  other  cases.  These  examples 
are  the  better  because  they  relate  not  only  to  crystalline 
rock — the  material  under  discussion — but  to  as  repre- 
sentative a  class  of  rock  as  could  be  selected.  Under  the 
shrinkage  tension  of  cooling,  the  rock,  as  it  forms,  parts 
along  planes  that  radiate  from  the  points  where  the 
greatest  tensions  have  been  developed.  The  parting 
planes  are  normally  three  in  number  and  these  diverge 
at  angles  of  about  120°  (see  Fig.  28).  As  these  planes 
are  extended,  they  intersect  one  another  and  divide  the 
whole  mass  into  six-sided  columns.  It  is  a  matter  of 
special  interest  that  the  edges  of  the  columns  are  habitu- 
ally raised,  as  shown  in  Fig.  27,  and  the  center  depressed. 
At  the  angles  there  are  sometimes  specially  raised  por- 
tions as  shown  in  Fig.  29,  giving  what  has  been  called  a 
"ball-and-socket"  structure.  All  these  special  features 
appear  in  modified  forms  in  the  application  to  the  earth- 
body,  as  we  shall  see. 

This  classical  case  embodies  the  principle  that  where 
tensional  stresses  are  concentrated  about  a  given  point 
or  column,  the  most  natural  mode  of  relief  is  a  partition 
of,  the  mass  into  three  sub-equal  parts  radiant  from  the 


THE  JUVENILE  SHAPING  OF  THE  EARTH      187 

point  of  greatest  stress.  There  is,  not  unnaturally,  much 
variation  in  the  actual  divisions  of  nature,  as  shown  in 
mud  cracks  in  particular,  where  the  working  factors  are 
variable.  The  process  is  simply  a  mechanical  accommo- 
dation to  existing  stresses  and  the  result  depends  much 
on  the  homogeneity  of  the  material  and  the  uniformity 
of  distribution  of  the  stresses.  It  is  not  a  crystalline 
process  and  the  forms  produced  by  it  are  quite  lacking 
in  the  refined  accuracy  of  crystalline  structures. 


FIG.  27  FIG.  28  FIG.  29 

FIGS.  27-29. — Fig.  27,  sketch  of  sections  of  basaltic  columns  from 
Giant's  Causeway  on  the  coast  of  Ireland.  (Chamberlin  arid  Salisbury 
Geology, 1, 476);  Fig.  28,.diagram  illustrating  the  system  of  partition  in 
the  first  stages  of  the  formation  of  basaltic  columns.  (Chamberlin  and 
Salisbury,  Geology,  I,  476) ;  Fig.  29,  diagram  showing  not  only  the  raised 
edges  of  the  columns  (shown  also  in  Fig.  27),  but  special  elevations  at 
the  angles,  giving  "  ball-and-socket  joints."  (After  Scrope.) 

Now  in  rotational  accommodation,  the  tensional 
stresses  that  probably  took  precedence  in  the  polar 
regions  and  were  most  intense  at  the  poles  would,  under 
this  law  of  partition,  be  eased  most  naturally  by  three 
fissure  tracts  radiating  from  the  poles  at  angles  of  the 
general  order  of  120°,  but  no  doubt  varying  considerably 
from  the  ideal.  These  radiating  fissure  tracts  should 
theoretically  be  terminated  at  the  fulcrum  zone,  for 
beyond  that  the  stresses  would  be  reversed.  The  effect 
would  be  to  divide  the  circumpolar  areas  into  three  great 


i88  THE  ORIGIN  OF  THE  EARTH 

segments  of  triangular  form  with  their  apexes  at  the 
pole  and  their  bases  on  the  fulcrum  zone. 

Now  each  polar  unit  must  have  acted  reciprocally  with 
an  equatorial  unit  of  the  same  value  in  any  rotational 
change.  It  seems  obvious  that,  if  three  great  triangular 
segments  had  been  thus  denned  in  the  polar  regions, 
each  reaching  to  the  fulcrum  zone  not  far  from  30° 
latitude,  the  simplest,  the  most  symmetrical,  the  most 
natural  reciprocal  working  mates  for  these  would  have 
been  three  similar  triangular  segments  set  in  reversed 
positions  with  their  bases  on  the  fulcrum  zone  and  their 
apexes  in  the  opposite  direction.  They  would  then  be 
peculiarly  fitted  to  seesaw  across  the  fulcrum  zone,  and 
that  was  the  nature  of  the  motion  required  in  response 
to  changes  of  rotation.  The  apex  of  the  equatorial 
triangles  would  thus  fall  in  the  fulcrum  zone  of  the 
opposite  hemisphere.  The  pairs  of  triangles  lying  base 
to  base,  each  wholly  in  one  of  the  reciprocating  tracts 
and  each  under  stress  to  yield  what  the  other  demanded, 
almost  ideally  fulfil  the  requirement  of  the  case.  The 
flexures  in  the  reciprocating  triangles  would  not,  to  be 
sure,  be  quite  alike,  but  their  working  values  would  be 
the  precise  complements  of  one  another. 

Geologic  history  affords  evidence  that  the  two  hemi- 
spheres have  taken  precedence  in  opposite  lines,  the 
southern  in  downward  movement  resulting  in  prevalent 
seas,  the  northern  in  upward  movement,  relatively, 
resulting  in  prevalent  land.  This  seems  to  have  been  a 
fixed  secular  difference  from  Archean  times  to  the 
present;  it  gives  ground  for  supposing  that  one  hemi- 
sphere, or  the  other,  took  precedence  in  the  tri-segmenta- 
tion  just  described.  Whichever  it  was,  the  divisions 


THE  JUVENILE  SHAPING  OF  THE  EARTH      189 

in  the  other  hemisphere  would  have  been  partially 
defined  by  such  precedent  action,  and  this  partial 
definition  should  have  guided  the  completion  of  the 
definition.  Now  the  three  pairs  of  reciprocating  tri- 
angles developed  from  the  pole  that  took  precedence 
appropriated  half  the  equatorial  belt,  in  saw-tooth 
fashion,  leaving  the  other  half  already  defined  in  reversed 
saw-tooth  form  to  mate  with  similar  reciprocating 
triangles  developed  from  the  opposite  pole,  only  the 
polar  lines  being  needed  to  complete  their  definition. 
This  done,  the  globe  would  be  divided  into  six  working 
pairs  of  triangular  segments,  the  salients  of  the  three  in 
one  hemisphere  dovetailing  neatly  into  the  re-entrants  of 
the  three  in  the  opposite  hemisphere.  The  zigzag  divi- 
sion of  the  equatorial  belt  had  the  advantage  of  giving 
it  superior  flexibility.  As  a  simple  adaptive  working 
device,  this  partition  seems  to  admit  of  no  rival.  Each 
triangular  pair  formed  a  quadrilateral,  and  this  term 
will  be  convenient  in  tracing  out  the  topographic  results, 
since,  in  the  main,  each  working  pair  gave  a  common 
physiographic  product,  though  there  was  some  tendency 
to  division  also  along  the  fulcrum  zone. 

It  has  been  convenient  to  sketch  this  divisional  process 
as  though  it  were  superficial,  but  we  must  hasten  to 
observe  that  the  deformation  involved  the  whole  earth. 
The  rotational  stresses  extended  to  the  heart  of  the 
earth  and  grew  in  intensity  in  that  direction.  The 
sides  of  the  reciprocating  pairs  of  triangles,  or  the 
quadrilaterals,  are  to  be  pictured  as  extending  to  the 
center  of  the  earth.  Thus  extended,  they  constitute 
four-sided  pyramids  with  their  apexes  at  the  earth's 
center.  Each  adjustment  to  a  new  rate  of  rotation  may 


I  go  THE  ORIGIN  OF  THE  EARTH 

then  be  pictured  as  a  north-south  swaying  of  these 
pyramids  on  their  apexes  attended  by  the  requisite 
upwarp  and  down-warp  of  the  reciprocating  halves, 
and  this  picture  is  peculiarly  appropriate  to  a  body  pre- 
disposed to  move  as  a  solid  mass.  This  seems  to  be  the 
simplest  mode  of  adjustment  available  for  such  a  recip- 
rocal deformation  in  such  a  solid  spheroidal  mass.  Its 
simplicity  and  its  adaptation  to  its  special  function  are 
perhaps  its  strongest  credentials. 

ADAPTATION   TO   TIDAL  ACTION 

This  segmentation  of  the  solid  earth-body  lends  itself 
happily  to  the  feeble  tidal  deformations  that  were  forced 
upon  the  earth  in  constant  bi-daily  succession.  The 
internal  stresses  of  the  body  tides  have  the  same  dis- 
tribution as  those  of  rotation,  according  to  Sir  George 
Darwin.6  While  the  tidal  cones  are  constantly  shifting 
northward  and  southward,  their  mean  position  is 
astride  the  equator.  In  this  position  they  reach  to 
about  60°  N.  Lat.  and  60°  S.  Lat.  At  the  poles  the 
mean  effect  is  perpetual  depression;  this  would  be 
constant  if  the  tides  did  not  shift  in  latitude.  As 
pointed  out  in  the  study  of  solar  eruptions,  the  tidal 
cones  represent  the  lifting  effect  of  the  tidal  forces.  As 
they  sweep  about  the  equator,  in  their  semi-diurnal 
courses,  the  equatorial  ends  of  the  diamond-shape 
segments  rise  and  fall  through  nearly  the  maximum 
amplitude  of  the  tidal  effect,  while  the  mean  movements 
of  the  polar  ends  are  low  and  at  the  polar  angles  theo- 
retically zero.  The  mean  oscillations  of  the  east  and 
west  sides  are  intermediate  in  value.  These  differences 
of  movement  are  probably  exaggerated  by  the  relations 


THE  JUVENILE  SHAPING  OF  THE  EARTH      191 

of  the  two  ends  of  the  oscillating  segments.  The  polar 
ends  are  snugly  wedged  together  and  mutually  aid  one 
another  in  approximating  zero  movement.  The  equa- 
torial ends  join  their  partners  of  the  opposite  hemisphere 
along  a  zigzag  line  of  notable  flexibility  which  offers 
much  larger  opportunities  for  accommodation  to  mutual 
motion.  The  tidal  movement  involves  an  internal 
tortional  strain  in  each  segment  and  yield  takes  place 
with  greatest  facility  in  the  equatorial  ends.  Recent 
tidal  studies  at  Potsdam  by  Hecker,  and,  more  com- 
pletely and  decisively,  at  Lake  Geneva  by  Michelson4 
and  colleagues,  have  shown  that  the  earth-body  yields 
more  in  a  north-south  direction  than  in  an  east-west 
direction.  This  suggests  that  perhaps  the  segmentation 
imposed  on  the  young  earth  by  rotation,  and  periodically 
revived  ever  since  by  changes  in  rotation,  by  tidal  strains, 
by  the  indirect  effects  of  shrinkage,  and  other  agencies 
of  deformation,  may  offer  the  mechanism  out  of  which 
this  difference  grows,  in  whole  or  in  part.  Reciprocally 
the  phenomenon  of  superior  north-south  flexibility  lends 
support  to  the  suggestion  already  advanced  that  ease- 
ment zones  of  rather  free  yield  were  developed  by  the 
repeated  movements  imposed  by  the  early  rotational 
stresses  and  that  the  mild  stresses  of  the  body  tides,  the 
rotational  stresses  incident  to  shrinkage,  and  perhaps 
the  stresses  incident  to  general  loading  and  unloading 
have  served  to  keep  these  in  working  function. 

EMBRYONIC    FRAMEWORK    OF    THE    INFANTILE    EARTH    A 
BASIS   OF  GROWTH 

If  the  earth  were  segmented  in  this  way  to  accommo- 
date the  recurrent  stresses  imposed  by  changes  of  rate 
of  rotation,  abetted  by  the  semi-daily  pulsations  of 


IQ2  THE  ORIGIN  OF  THE  EARTH 

the  body  tides  and  by  periodic  shrinkage;  and  if  the 
main  easement  zones  lay  between  the  quadrilaterals 
so  defined,  the  fissurings,  faultings,  foldings,  and  other 
special  features  of  deformation  forced  by  the  tensions 
and  compressions  of  the  required  readjustments  would 
chiefly  lie  along  the  segment  borders  and  the  general 
effect  would  be  elevation,  and  in  general  the  elevation 
would  be  greatest  at  the  angles,  where  three  lines  of 
disruption  join.  In  this  there  would  be  close  accord 
with  the  surface  shaping  of  sides  of  basaltic  columns 
which  are  raised  at  the  edges  and  especially  at  the  angles, 
as  shown  in  Figs.  27  and  29.  The  easements  of  second- 
ary stresses  would  take  their  departures  from  these 
borders  and  especially  from  these  angles.  An  excep- 
tional portion  of  the  lavas  forced  from  the  interior 
would  naturally  find  exit  along  these  border  tracts  of 
disruption  and  would  aid  in  building  them  up  with 
relatively  light  material.  Thus  an  embryonic  frame- 
work was  established,  and  naturally  became  the  basis 
of  subsequent  growth  for  the  protrusive  portion  of  the 
earth.  It  was,  of  course,  at  all  subsequent  times, 
peculiarly  subject  to  denudation,  disruption,  depression, 
coalescences,  and  other  forms  of  obscuration,  but  yet,  in 
its  mutilated  forms,  it  should  be  traceable  in  the  salient 
configurations  of  the  earth  even  in  its  adult  form. 

The  disruptions  on  the  borders  of  the  segments  would 
tend  to  shift  the  accumulating  waters  toward  their 
interiors  which,  if  we  may  trust  theory  and  the  example 
of  the  basaltic  columns,  mud-cracks,  and  like  phe- 
nomena, should  have  been  relatively  sunken  at  the  out- 
set. By  interpretation,  the  primary  delineation  of  the 
oceans  was  thus  instituted.  The  outlines  thus  deter- 


THE  JUVENILE  SHAPING  OF  THE  EARTH      193 

mined  would,  in  their  turn,  be  subject  to  modifications  as 
they  grew. 

In  both  cases,  the  modifications  should  have  been 
many  and  profound  and  they  cannot  here  be  more  than 
alluded  to  summarily.  The  atmosphere  had  the  first 
handling  of  all  the  incoming  material,  as  already 
remarked.  The  hydrosphere  took  a  second  hand.  The 
shrinkage  diastrophism  sprang  chiefly  from  the  accessions 
thus  controlled.  It  should  not  be  a  source  of  surprise  if 
these  three  powerful  agencies  shall  be  found  to  have 
wrought  not  a  few  profound  distortions  in  the  infantile 
framework,  to  have  built  out  not  a  few  apophyses 
marked  by  peculiarities  of  their  own,  and  to  have 
weakened  or  destroyed  some  sections  of  the  primitive 
framework.  Coalescences  of  parts  of  the  ideal  structure 
will  naturally  have  obscured  other  features.  Even  if 
space  permitted,  it  would  not  befit  our  theme — which 
is  genesis  rather  than  evolution — here  to  enter  upon  a 
delineation  of  this  complex  of  formative  actions;  it 
belongs  to  the  adolescent  history  of  the  earth  rather  than 
to  its  genesis.  We  may  properly  go  only  so  far  as  to 
see  the  process  under  way — that  much  may  be  regarded 
as  genetic. 

MODIFYING  ATMOSPHERIC  INFLUENCES 

Planetesimal  accessions  could  reach  the  earth  only  by 
way  of  the  atmosphere.  Their  final  lodgment  depended 
on  its  action.  Its  dominant  movements-  are  ascent  and 
descent;  its  north-south  circulation  is  a  minor  factor. 
Essentially  half  the  atmosphere  is  ascensive  and  half 
decensive ;  this  must  always  have  been  so  in  the  nature 
of  the  case.  The  ascending  currents  tended  to  buoy 


194  THE  ORIGIN  OF  THE  EARTH 

up  the  planetesimal  dust,  while  the  descending  currents 
tended  to  bring  it  down.  The  turbulence  of  the  decen- 
sive  air  near  the  surface,  however,  delayed  the  actual 
lodgment  of  the  dust  and  held  some  part  of  the  lighter 
portion  in  suspension  until  it  drifted  into  regions  of 
ascensive  currents.  Descending  air  is  habitually  dry 
and  the  flotation  of  dust  in  it  is  notably  protracted. 
Such  protracted  flotation  necessarily  had  a  sifting 
effect,  favoring  the  lodgment  of  particles  of  greater 
weight  in  proportion  to  surface,  while  those  of  lesser 
weight  to  surface  were  held  longer  in  suspension  and 
more  largely  carried  by  the  horizontal  component 
of  the  air  currents  into  neighboring  tracts  where  ascensive 
currents  prevailed.  It  is  inferred,  therefore,  that  some 
small  measure  of  preponderance  of  planetesimals  and 
planetesimal  dust  of  the  higher  specific  gravity  found 
lodgment  beneath  the  descending  currents.  It  is  not 
supposed  that  the  sifting  action  would  be  more  than  very 
partial,  or  that  the  resulting  difference  in  specific  gravity 
of  the  deposit  would  be  more  than  very  slight. 

As  the  main  outlines  of  land  and  sea  are  assumed  to 
have  been  already  defined  by  the  embryonic  framework 
imposed  by  rotational  diastrophism,  and  to  have  coin- 
cided more  or  less  closely  with  the  borders  of  the 
primitive  segments,  the  fundamental  features  of  the 
atmospheric  circulation  should  have  been  controlled  by 
these  outlines  and  hence  have  been  then  as  much  as  now. 
The  areas  of  dominantly  high  barometer  and  of  descend- 
ing air  should  have  centered,  as  now,  over  the  great  basins, 
in  the  main.  These  portions  of  the  growing  earth  thus 
came  to  preponderate  in  specific  gravity,  in  some  slight 
degree. 


THE  JUVENILE  SHAPING  OF  THE  EARTH      195 

The  planetesimal  material  that  floated  longer  and 
reached  areas  of  ascending  currents,  where  the  air  had  a 
precipitating  tendency,  was  brought  down  by  rain  and 
snow  chiefly.  This  tended,  in  some  measure,  to  con- 
centrate the  dust  of  lower  specific  gravity  in  the  areas 
of  ascending  air.  We  are  thus  forced  to  take  into 
account  the  essential  features  of  the  atmospheric  circula- 
tion, since  that  seems  to  have  played  an  important  part  in 
the  distribution  of  specific  gravities  in  the  growing  earth. 

The  most  fundamental  feature  of  the  horizontal  cir- 
culation in  the  juvenile  ages  probably  had,  as  now,  a 
twofold  aspect,  an  equatorial  belt  of  easterly  winds, 
flanked  on  either  side  by  high-latitude  zones  of  westerly 
winds,  the  easterly  and  westerly  components  being 
deflections  from  a  meridional  circulation  forced  by  high 
temperature  in  the  torrid  zone  and  low  temperature  in 
the  frigid  zones.  There  are  some  suggestive  analogies 
between  these  interchanges  between  the  torrid  and 
the  frigid  zones,  and  the  reciprocating  equatorial-polar 
action  of  the  lithosphere,  both  being  products  of  rota- 
tion. Both  have  transition  zones  not  far  from  30° 
latitude.  In  the  atmosphere,  there  was  convergence  and 
crowding  of  air  currents  toward  the  poles,  and  divergence 
and  deployment  toward  the  equator,  which  forced  a 
secondary  adjustment  of  the  circulation  analogous  to  the 
secondary  deformative  effects  of  rotation.  This  second- 
ary atmospheric  circulation  is  now  tripartite,  and 
probably  always  was  so,  because  a  threefold  division 
best  accommodated  the  currents  to  the  peculiar  spatial 
requirements  of  a  hemisphere.  The  tripartite  features 
of  hemispherical  circulation  are  not  very  declared  or 
impressive  unless  attention  is  directed  to  them,  since 


196  THE  ORIGIN  OF  THE  EARTH 

they  are  masked  by  the  primary  features,  but  yet 
they  are  very  real  and  are  highly  important  theoreti- 
cally and  economically.  They  form  bi-zonal  cycles,  or, 
to  use  a  looser  term  that  better  fits  their  nature,  bi-zonal 
gyrals.  They  are  analogous  to  the  three  reciprocating 
segments  imposed  by  rotation  on  the  lithosphere,  and 
they  are  very  similarly  placed.  They  embrace  the 
chief  " permanent  highs,"  and  their  western  borders 
are  defined,  at  intervals,  in  a  spectacular  way,  by  the 
tracks  of  the  greatest  of  the  tropical  hurricanes.  Ob- 
scurely denned  belts  of  currents  swing  about  the  perma- 
nent highs  and  form  the  most  important  surface  element 
in  the  atmospheric  interchange  between  high  and  low 
latitudes.  Five  of  such  gyral  systems  are  fairly  well 
characterized,  one  in  the  North  Pacific,  on  which 
Eastern  Asia  depends  for  much  of  its  fertility,  one  in  the 
South  Pacific,  that  gives  prosperity  to  Eastern  Australia, 
one  in  the  Indian  Ocean  north  of  the  equator,  affecting 
Southern  Asia,  and  one  also  south  of  the  equator, 
affecting  East  Africa,  and  one  in  the  North  Atlantic 
Ocean,  on  which  the  prosperity  of  the  eastern  half 
of  North  America  largely  depends.  The  South  Atlantic 
develops  its  appropriate  area  of  high  pressure  and  its 
circulatory  loop,  but  not  the  typhoon  phenomena. 
These  great  gyrals  are  believed  to  be  fundamental 
features  of  terrestrial  circulation,  due  more  to  the  in- 
herent dynamics  of  circulation  than  to  the  configurations 
of  land  and  sea,  though  the  two  agencies  are  co-operative 
and  the  physiographic  configurations  perhaps  locate 
the  gyrals.  If  fundamental  features,  they  doubtless  had 
their  place  in  the  circulation  from  the  outset.  To  be 
sure,  they  seem  to  be  determined  now  by  the  great 


THE  JUVENILE  SHAPING  OF  THE  EARTH      197 

features  of  land  and  sea,  but  they  are  perhaps  only 
localized  by  them.  If  strictly  dependent  on  topographic 
features,  the  juvenile  reliefs  of  the  lithosphere  on  the 
borders  of  the  primary  segments  were  probably  sufficient 
to  make  them  features  of  the  juvenile  circulation. 

The  effect  of  these  bi-zonal  systems  of  circulation  is 
to  cut  the  30°  zone  of  dominantly  descending  circulation 
into  three  segments  and  to  give  the  belt  a  beaded  form 
well  shown  on  modern  meteorological  maps,  especially 
those  of  the  Southern  Hemisphere,  where  symmetry  pre- 
vails and  the  deployment  is  most  nearly  normal.  The 
superior  accession  of  planetesimal  dust  of  high  specific 
gravity  due  to  descending  currents  was  thus  measurably 
bunched  in  the  hearts  of  these  bi-zonal  gyrals — in  other 
words,  in  the  areas  of  high  atmospheric  pressure  over 
the  oceans. 

MODIFYING   HYDROSPHERIC  INFLUENCES 

The  broad  features  of  the  juvenile  hydrosphere  must 
have  been  determined  by  the  reliefs  of  the  lithosphere, 
the  embryonic  framework,  and  this,  by  hypothesis,  had 
been  given  its  basal  features  by  rotation.  The  circula- 
tion of  the  atmosphere  probably  in  all  ages,  as  now, 
gave  direction  to  the  ocean  currents.  Whatever 
planetesimal  dust  fell  into  the  oceans  no  doubt  floated 
even  longer  than  in  the  air  and  was  more  effectively  dis- 
tributed over  the  areas  embraced  within  the  ocean  circu- 
lation. The  evolution  of  the  oceans  doubtless  always 
tended  toward  circularity  of  outline;  their  primary 
effect  on  the  dust  delivered  to  them  by  the  air  was  an 
increased  circularity  in  its  distribution.  In  so  far  as 
the  atmosphere  was  predisposed  to  deposit  its  dust 


198  THE  ORIGIN  OF  THE  EARTH 

in  belts,  the  oceans  measurably  thwarted  this  tendency 
and  gave  the  dust  a  more  circular  distribution.  We 
have,  however,  just  observed  that  the  atmosphere, 
though  primarily  belted,  is  measurably  suborganized  into 
three  cyclical  divisions,  centered  now — and  probably 
always — over  the  oceans.  The  notable  concentrations 
of  descending  air,  at  present,  lie  over  the  three  oceanic 
sections  of  the  30°  belt  of  descending  air.  To  somewhat 
similar  concentrations  in  juvenile  times,  the  first  step 
toward  the  concentration  of  the  denser  material  is 
assigned;  the  ocean  circulation,  to  which  this  was  next 
committed,  advanced  the  work  a  step  farther  by  its 
cyclic  action..  In  this  combination  lies  an  assignable 
first  reason  for  the  higher  specific  gravity  of  the  sub- 
oceanic  segments,  an  important  fact  now  well  established 
by  geodetic  and  other  evidence.  In  Figs.  30-38  we 
have  introduced  ovals  within  the  six  segments  to  empha- 
size the  element  of  circularity  interpreted  as  having 
been  imposed  by  the  atmospheric  and  hydrospheric 
agencies  on  the  original  quadrilateral  outline  assigned  to 
rotational  stresses. 

To  these  primitive  agencies  that  took  part  in  localizing 
the  denser  and  the  lighter  planetesimals,  respectively, 
there  were  added  secondary  agencies  that  further 
effected,  in  a  mild  but  systematic  way,  the  distribution 
of  specific  gravity  in  the  growing  earth. 

SECULAR    PERPETUATION    OF    DIFFERENCES    OF    SPECIFIC 

GRAVITY 

During  all  the  stages  of  growth,  the  planetesimals  that 
fell  into  the  waters  were  measurably  preserved  from 
decomposition,  while  those  that  fell  on  the  land  suffered 


THE  JUVENILE  SHAPING  OF  THE  EARTH      199 

weathering  and  wash.  The  dissolved  portions  were 
added  to  the  oceans,  and  either  remained  in  solution 
in  their  waters  or  were  deposited  on  their  bottoms. 
The  residual  matter  was  left  as  a  lodgment  product 
on  the  land  or,  more  largely,  was  laid  down  close  about 
the  land  as  sub-sea  terraces.  In  the  final  state  reached 
by  these  several  portions  after  deep  burial  and  meta- 
morphism,  the  residuum  left  on  or  about  the  land  appar- 
ently came  to  have  somewhat  less  specific  gravity  than 
the  part  added  to  the  ocean  segments.  The  secular 
processes  seem  thus  to  have  tended  to  perpetuate  the 
superior  density  of  the  sub-oceanic  segments  and  the 
greater  levity  of  the  continental  segments  inherited  from 
the  previous  processes.  At  the  same  time,  matter  was 
constantly  being  added  to  the  basins  at  the  expense  of 
the  land.  It  is  hence  inferred  that  the  sub-oceanic 
segments  were  habitually  urged  to  sink,  while  the  conti- 
nents were  forced  to  rise  to  restore  the  equilibrium. 
This  constitutes  an  enduring,  though  not  an  indefinitely 
enduring,  basis  for  isostatic  action,  because  the  actuat- 
ing differentiation  is  deeply  inbred  in  the  formation  of 
the  earth. 

During  all  the  ages  of  growth,  the  winds  swept  por- 
tions of  the  light  dust  of  the  surface  from  windward 
to  leeward,  and  thus  shifted  material  of  low  specific 
gravity  in  given  directions  and  modified  the  growth  of  the 
lands  as  well  as  the  distribution  of  specific  gravity. 
The  streams  and  the  ocean  currents  aided  even  more 
effectively  in  giving  direction  to  the  growth  of  the  lands 
and  in  modifying  the  configuration  inherited  from 
rotational  accommodation,  while  they  incidentally 
affected  the  specific  gravities.  So,  also,  the  diastrophism 


200  THE  ORIGIN  OF  THE  EARTH 

that  sprang  from  shrinkage  and  other  sources  cast  in  its 
contributions  periodically,  while  vulcanism  added  its 
more  or  less  adventitious  work.  Probably  both  shrink- 
age deformations  and  vulcanism  were  much  influenced 
by  the  structural  effects  and  deformative  alignments 
handed  down  from  previous  rotational  action,  but,  never- 
theless, they  doubtless  lent  their  own  influences  toward 
shaping  the  surface  features.  The  final  physiographic 
configurations  now  presented  for  study  are  thus  to 
be  interpreted  as  the  joint  product  of  a  complex  of 
agencies  working  together  through  the  whole  eon 
that  spanned  the  growth  of  the  earth  from  the  modest 
dimensions  of  its  infancy  to  the  full  measure  of  its 
maturity.  In  our  analysis,  the  rotational  factor  is 
held  to  have  contributed  the  embryonic  framework  on 
which  the  other  shaping  agencies  built  their  syste- 
matic and  their  adventitious  growths,  each  in  its  own 
fashion. 

BASAL  FEATURES  OF  THE  GREATER  CONFIGURATIONS 

To  justify  the  foregoing  deductions,  the  embryonic 
framework  of  the  earth  should  be  traceable,  even  at 
the  present  time,  in  its  master-features  at  least,  how- 
ever much  they  may  be  disguised  by  the  effects  later 
superposed  by  other  agencies,  for  fundamental  elements 
bearing  such  distinctive  characteristics  could  scarcely 
be  wholly  obliterated  by  subsequent  events  or  be  the 
products  of  accident.  Besides,  the  disguising  factors 
should  bear  their  own  characteristics,  and  these  should 
show  some  relations  to  the  basal  factors.  It  will  aid 
in  tracing  the  embryonic  elements  if  the  leading  features 
that  mask  them  are  first  pointed  out. 


THE  JUVENILE  SHAPING  OF  THE  EARTH      201 

It  seems  clear  that  the  southern  half  of  the  earth-body 
is  formed  of  heavier  material  than  the  northern  half,  for 
this  is  implied  by  the  greater  mass  of  water  drawn  into 
the  Southern  Hemisphere  and  the  greater  depressions 
that  have  taken  place  there,  these  two  results  being  the 
joint  effects  of  a  common  cause.  This  dominance 
is  naturally  expressed  in  fewer  and  simpler  yield- tracts. 
The  embryonic  lines  should  there  be  least  distorted. 
But  a  broad  trough,  apparently  arising  from  an  inter- 
vening cause,  lies  between  35°  and  65°  S.  Lat.,  encircling 
the  globe  and  holding  the  southern  seas.  This  is  to  be 
regarded  as  having  depressed  and  disguised  the  three 
radial  yield-belts  that,  in  the  ideal  scheme,  should  have 
diverged  from  the  South  Pole  in  response  to  rotational 
stresses. 

The  Northern  Hemisphere  is  clearly  the  yield-partner 
of  the  Southern  Hemisphere;  as  such,  it  has  been 
squeezed  up,  while  its  partner  was  depressed;  it  is  hence 
more  distorted  and  stands  forth  above  the  sea-level  more 
notably.  The  crust  is  here  more  broken  and  more 
diversified  by  folds,  faults,  and  other  striking  forms  of 
relief.  The  zone  between  40°  and  70°  N.  Lat.  is  about 
as  markedly  protrusive  as  that  between  35°  and  65°  S. 
Lat.  is  markedly  depressed.  In  harmony  with  these 
contrasts,  the  radial  yield-lines  of  the  north  polar  region 
show  notable  distortion  and  deflection.  As  to  the 
cause  of  these  contrasted  northern  and  southern  features, 
tentative  views  are  entertained,  but  they  are  too  imma- 
ture and  too  much  aside  from  our  main  theme  to  find 
a  place  here.  While  these  causes  were  probably  in- 
herited, in  a  germinal  sense,  from  the  primitive  agencies, 
their  main  effects  seem  to  be  referable  rather  to  later 


202  THE  ORIGIN  OF  THE  EARTH 

than  to  earlier  stages  of  deformation  and  hence  they 
are  superposed  and  tend  to  obscure  the  fundamental 
features. 

It  is  logical  to  look  rather  to  the  Southern  than  to  the 
Northern  Hemisphere  for  the  simplest  and  least  dis- 
guised outlines  of  the  primitive  framework,  for  the 
heavy  master-segments  are  naturally  less  subject  to  dis- 
tortion than  the  yield-segments.  So,  in  turn,  there  is 
reason  to  look  to  the  Northern  Hemisphere  for  a  more 
marked  expression  of  divergencies  and  of  superadded 
effects  assignable  to  the  work  of  the  co-operating 
agencies.  This  is  especially  true  of  such  agencies  as 
were  dependent  on  protrusion  for  their  efficiency,  for 
example,  erosion,  transportation,  and  deposition,  which 
led  to  outgrowths  from  the  yield-tracts  and  which  also, 
by  loading  and  unloading,  led  to  deformation. 

Lying  between  these  high-latitude  belts  of  the  two 
hemispheres,  the  equatorial  belt  should  show  inter- 
mediate proportions  of  elevation  and  depression,  but 
here  the  characteristic  lines  of  the  embryonic  framework 
are  oblique,  not  meridional,  and  are  so  fundamental 
that  they  should  show  through  all  disguises  and  con- 
stitute a  decisive  criterion. 

A  source  of  superficial  disguise  by  outgrowths  and  dis- 
placements— springing  probably  also  from  the  prepon- 
derant specific  gravity  of  the  Southern  Hemisphere — is 
the  lower  temperature,  and  hence  dominant  force,  of  the 
atmosphere  of  the  Southern  Hemisphere,  probably 
the  result  of  the  larger  water  surface  and  the  scantier 
lands  of  that  hemisphere.  If  thus  caused,  the  pre- 
ponderance probably  extended  far  backward  and  con- 
ditioned at  least  the  later  growth  of  the  earth.  As  a 


THE  JUVENILE  SHAPING  OF  THE  EARTH      203 

result  of  this,  the  thermal  equator  lies,  and  probably  has 
lain  throughout  the  geologic  ages,  north  of  the  rotational 
equator,  so  that  the  ancestral  circulation  of  the  Southern 
Hemisphere  was,  as  now,  relatively  free,  full,  and  syste- 
matic, while  that  of  the  Northern  Hemisphere  was 
cramped  and  distorted.  The  out-building  from  the 
embryonic  framework  in  the  Southern  Hemisphere  was 
therefore  relatively  free  from  idiosyncrasies;  that  in 
the  Northern  Hemisphere  much  more  peculiar  and 
divergent.  Leeward  out-building  might  well  have 
been  pronounced  where  the  primitive  lands  were  large; 
the  framework  might  well  show  peculiar  eastward- 
trending  apophyses  in  the  middle  and  high  latitudes.  In 
the  equatorial  belt,  the  outgrowths  might  naturally 
appear  as  westward  accessions;  the  broad  westward- 
facing  noses  of  Africa,  South  America,  and  Australia  are 
perhaps  the  cumulative  effects  of  the  recurving  circula- 
tion of  the  three  great  atmospheric  gyrals  referred  to  in  a 
preceding  paragraph.  They  are  among  the  most  singular 
apophyses  anywhere  attached  to  the  embryonic  frame- 
work. The  interpretation  of  the  details  of  the  outgrowth 
from  the  framework  is  quite  as  fascinating  as  the  tracing 
out  of  the  more  basal  lines,  but  it  belongs  rather  to  later 
geology  than  to  genesis. 

The  protrusive  effects  of  rotational  stresses  should 
have  been  mainly  felt  at  the  angles  where  the  yield-tracts 
joined  one  another;  subordinately  along  the  yield- 
tracts  themselves.  The  continents  should  therefore 
have  grown  up  from  these  angles  as  centers,  and  have 
been  guided  by  the  yield-tracts,  and  by  the  co-operating 
agencies  in  their  extensions.  In  the  Southern  Hemi- 
sphere, it  will  be  seen  that  the  growth  was  mainly 


204  THE  ORIGIN  OF  THE  EARTH 

northward,  or  toward  the  yield-hemisphere  in  the 
dominant  direction  of  wind  and  current  movements,  and 
that  it  took  place  mainly  between  the  bifurcating  lines 
of  the  yield-tracts  (see  in  particular  Figs.  32  and  33).  In 
the  Northern  Hemisphere,  the  growth  will  be  seen  to  have 
been  mainly  northward  also,  and  notably  eastward,  or 
leeward,  in  the  higher  latitudes.* 

In  addition  to  these  obscuring  features  of  conti- 
nental development,  we  have  yet  to  take  into  account 
the  diastrophism  that  sprang  from  secular  loading 
and  unloading,  and  from  the  shrinkage  of  the  earth- 
body  which  appears  to  have  assumed  the  leadership 
in  shaping  the  earth  after  growth  ceased,  but  let  this 
rest  for  the  present.  Let  us  turn  now  to  the  tracing 
of  the  embryonic  framework  beneath  these  obscuring 
features : 

i.  Starting  with  the  dominant  hemisphere,  there 
should  be  three  yield-tracts  diverging  at  wide  angles 
from  the  South  Pole,  all  directed  northward  toward 
the  fulcrum  zone.  When  this  is  reached,  the  chief 
yield- tracts  should  fork,  or  at  least  turn  at  a  pro- 
nounced angle,  and  strike  obliquely  across  the  equatorial 
zone  to  the  fulcrum  zone  of  the  Northern  Hemisphere, 
where  the  meridional  direction  should  be  resumed  and 
the  three  yield-tracts  converge  toward  the  North  Pole. 
These  are  singular  features  and  are  held  to  be  critical  and 
decisive. 

*  At  first  thought  geologists  will  be  disposed  to  challenge  this  because 
post-Cambrian  growth  has  often  been  in  a  different  direction,  but  it 
is  to  be  noted  that  the  later  growth  was  determined  by  the  persistent 
protrusion  of  the  regions  of  least  specific  gravity,  and  these  were  likely 
to  be  those  that  had  grown  most  by  eolian  and  aqueous  action  in  the 
earlier  stages. 


THE  JUVENILE  SHAPING  OF  THE  EARTH      205 

The  lines  from  the  South  Pole  to  the  zone  of  bifurca- 
tion or  angulation,  not  far  from  30°,  are  fairly  realized 
in  the  oft-cited  southward-pointing  extremities  of  Africa, 


FIG.  30. — South  polar  view  of  the  globe  showing  the  relations  of  the 
southern  points  of  South  America,  Africa,  and  Australia  to  Antarctica 
and  the  South  Pole,  and  the  tripartite  division  of  the  south  polar  region. 
The  radiant  lines  merely  suggest  the  approximate  positions  of  the  yield- 
tracts,  which  of  course  take  on  natural  flexures.  The  ovals  suggest  the 
somewhat  circular  configuration  of  the  oceans. 

Australia,  and  South  America  (see  Fig.  30).  These 
all  suffer,  to  be  sure,  from  the  circumpolar  sag  in  which 
the  southern  seas  lie,  but  all  of  them  are  connected  with 
Antarctica  by  sub-sea  features,  or  at  least  suggestions  of 


206  THE  ORIGIN  OF  THE  EARTH 

such  features,  and  there  is  much  biologic  evidence  tha 
there  were  more  ample  connections  in  the  early  geologi 
ages,  late  as  these  were  in  the  bodily  growth  of  th 
earth. 


FIG.  31. — South  Atlantic  view  of  the  globe,  showing  also  the  Soutl 
American  and  South  African  bifurcations  and  angulations  of  the  mail 
structure  lines  and  yield-tracts,  indicated  by  the  straight  lines  whicl 
outline  the  quadrilaterals  inclosing  the  oceans. 

2.  As  the  yield-tract  directed  toward  South  Ameria 
reached  the  fulcrum  zone,  or  its  vicinity,  its  angulatior 
and  bifurcation  are  strikingly  realized  (Fig.  31).  The 
main  continental  trend  turns  sharply  to  the  northwest 


THE  JUVENILE  SHAPING  OF  THE  EARTH      207 

while  there  branches  to  the  northeast  a  less  dominant 
but  important  structural  tract,  the  "  Backbone  of 
Brazil."  The  main  trend  to  the  northwest  holds 
strongly — overlooking  the  rounded  westward-facing 


FIG.  32. — Antillean  view  of  the  globe,  showing  the  northwest- 
southeast  trend  lines  and  their  angulations  with  the  meridional  trends  in 
the  high  latitudes  of  both  hemispheres. 

outgrowth — and  is  extended  in  good  alignment  through 
the  Isthmus  of  Panama,  the  Central  American  States, 
the  Antilles,  and  onward  into  the  United  States  to  the 
critical  zone  appropriate  for  a  reversed  angulation  into 
a  meridional  trend  (Fig.  32).  This  reversal  is  fairly 


208  THE  ORIGIN  OF  THE  EARTH 

well  expressed  in  structural  trends  which  hold  for  a  while, 
but  they  soon  become  obscured  by  deflections  and 
divergencies  referable  to  special  continental  deployment. 

From  the  point  of  first  angulation  in  South  America 
the  structural  belt  trending  to  the  northeast,  embracing 
the  "  Backbone  of  Brazil,"  suffers  a  break  where  the  two 
Atlantics  coalesce,  but  it  may  be  regarded  as  having 
a  recovery  and  a  continuation  in  the  structure  lines  that 
skirt  the  northwestern  border  of  Africa.  The  southwest- 
ern deflection  of  the  Atlas  range,  though  a  late  feature, 
was  perhaps  guided  by  the  old  yield-lines. 

3.  The  axis  diverging  from  the  South  Pole  toward 
Africa  seems  to  have  suffered  most  from  the  sag  under 
the  south  seas,  but  qn  entering  South  Africa  it  bifurcates 
in  about  the  appropriate  latitude,  and  two  ancient 
crystalline  terranes  strike  northeasterly  and  north- 
westerly, respectively,  nearly  parallel  to  the  two  flanks  of 
the  African  continent  (Figs.  31  and  33).  The  mutual 
divergence  of  these  tracts  falls  short  of  the  ideal  angle, 
suggesting  an  appression  from  the  sides.  This  suggestion 
is  in  harmony  with  the  configuration  assigned  the  whole 
quadrilateral  and  with  the  peculiarities  of  the  European 
segment.  It  is  also  in  harmony  with  the  notable  pro- 
trusion of  Africa  which,  throughout  geologic  history, 
so  far  as  known,  seems  to  have  been  the  most  uniformly 
protrusive  of  all  the  continents. 

At  about  the  appropriate  latitude  in  the  Northern 
Hemisphere,  the  northwest-trending  branch  of  the 
African  yield-tract  is  interpreted  as  angulating  to  the 
northward  and  following  the  general  direction  of  the  west 
border  of  Europe.  The  northeastward-trending  yield- 
tract  is  interpreted  as  angulating  in  the  opposite  direc- 


THE  JUVENILE  SHAPING  OF  THE  EARTH      209 

tion,  and  striking  northward  along  the  Ural  axis  toward 
the  North  Pole. 

4.  The  third  yield-belt  diverging  from  the  South  Pole 
seems  to  have  developed  two  subtracts  of  easement,  the 


FIG.  33. — View  of  the  Eurafrican  quadrilateral,  showing  its  somewhat 
appressed  form,  its  angulations,  and  the  Caspio-Mediterranean  cluster  of 
depressions  grouped  by  an  oval  after  the  method  used  to  indicate  the 
circularity  of  the  oceans. 

one  striking  toward  Australia,  the  other  toward  New 
Zealand  (Fig.  34).  On  reaching  the  fulcrum  zone,  both 
of  these  give  place  to  a  pronounced  group  of  northwest- 
trending  axes  striking  through  the  East  Indies  and  into 


210  THE  ORIGIN  OF  THE  EARTH 

Asia,  where,  at  the  appropriate  latitude,  they  reach  a 
most  remarkable  center  of  new  trends  which,  while 
northward,  are  affected  by  a  pronounced  deflection  to 
the  northeast.  The  northwest- trending  yield-tract 


FIG.  34*. — An  East  Indian  view  of  the  globe,  showing  the  dominant 
trend  lines  about  it  and  their  angular  relations  to  the  meridional  lines 
of  the  higher  latitudes,  north  and  south,  as  well  as  their  relations  to  the 
adjacent  great  basins. 

through  the  East  Indies  is  very  pronounced  and  highly 
complex,  but  a  northeastern  belt  is  not  developed. 
The  submerged  configuration  of  the  half-developed 
Australasian  continent  very  closely  resembles  that  of 


THE  JUVENILE  SHAPING  OF  THE  EARTH      211 

South  America.  The  yield-belt  that,  in  an  ideal  scheme, 
should  have  connected  Australasia  with  North  America 
is  replaced  by  an  apparent  coalescence — or  non-severance 
—of  the  North  Pacific  and  South  Pacific  basins,  more 
likely  their  non-severance  than  their  coalescence  after  an 
earlier  severance.  This  non-severance  is  analogous  to 
the  less  complete  effect  already  observed  between  the 
North  and  South  Atlantic.  The  suggestion  is  that 
where  two  quadrilateral  segments  in  opposite  hemi- 
spheres were  so  related  as  to  work  together  in  some  degree 
in  responding  to  rotational  changes,  it  was  possible  for 
them  to  remain  united  on  one  flank  provided  the  other 
moved  quite  freely  by  way  of  compensation.  Such 
free  movement  of  the  west  flank  seems  to  have  been  quite 
fully  realized  in  the  unusual  flexibility  of  the  East  India 
tract  standing  over  against  the  united  east  borders  of 
the  North  and  South  Pacific  (Fig.  34),  and  in  the  similar 
flexibility  of  the  West  Indies  in  compensation  for  the 
partial  union  of  the  North  and  South  Atlantic  on  the  east 
side  (Fig.  35).  If  this  interpretation  is  valid,  it  is  not 
strange  that  the  joint  Pacific  segment,  by  far  the 
greatest  of  all,  should  have  required  for  compensation  on 
its  western  side  so  marked  and  so  broad  a  tract  as  that 
embraced  between  the  two  lines  drawn  on  the  illustrative 
globe,  which  are  extended  to  each  pole. 

North  of  the  North  Pacific  segment  there  are  notable 
deviations  from  our  ideal  scheme.  The  most  notable 
of  these  is  the  Alaska-Siberian  bridge  between  the 
American  and  Asiatic  continents,  which  cuts  off  the 
apex  of  the  North  Pacific  quadrilateral.  The  present 
expression  of  this  is  late  in  origin.  If  the  initiation  of 
the  bridge  is  not  really  late  in  origin,  it  has  certainly  been 


212  THE  ORIGIN  OF  THE  EARTH 

strongly  accentuated  in  relatively  recent  geologic  times, 
and  so  it  is  perhaps  more  largely  referable  to  shrinkage 
diastrophism  than  to  embryonic  causes.  We  will  refer 
to  this  later. 


FIG.  35. — North  Atlantic  view  of  the  globe,  showing  the  relations 
of  the  coalescent  ocean  basins  to  the  yield-tracts  lying  west  of  them, 
particularly  those  of  the  West  Indies. 

While  this  and  other  divergencies,  shortcomings,  and 
overplacements  are  not  to  be  ignored,  the  prevailing 
obliquity  in  the  equatorial  belt  and  the  prevailing 
meridional  trend  in  the  higher  latitudes — especially  in 
the  dominant  hemisphere — are  so  pronounced  that  they 


THE  JUVENILE  SHAPING  OF  THE  EARTH      213 

can  scarcely  be  without  fundamental  significance.  Some 
of  the  incompleteness  of  expression  of  the  basal  frame- 
work is  perhaps  referable  to  a  phase  of  the  very  principle 
on  which  the  whole  segmentation  is  based,  viz.:  the 
tendency  of  rigid  bodies  to  concentrate  easement  move- 
ments in  zones  of  freest  yield  and  to  reduce  disruptive 
lines  elsewhere  to  the  minimum.  There  seem  to  be 
two  notable  expressions  of  this : 

1.  Diastrophic    movements   in   the   equatorial   belt 
seem  to  have  been  concentrated,  to  an  exceptional  degree, 
in  the  oblique  yield-tracts  so  conspicuous  in  the  East 
Indies  and  in  the  West  Indies,  both  of  which  habitually 
suffer  seismic  and  volcanic  disturbances  even  to  this 
day.     Unusual  -  flexibility  in  these  tracts,  on  the  west 
flanks  of  the  great  paired  oceans,  stands  over  against 
the  coalescence  of  the  North  and  South  Pacific,  and  the 
North  and  South  Atlantic  on  the  opposite  sides  of  their 
respective  segments,  as  already  noted;    and  so,  as  a 
result,  the  six  segments  of  the  ideal  scheme  coalesced 
partially  into  three  working  pairs,  and  so  the  ultimate 
working  segmentation  became  about  as  nearly  trifid  as 
hexafid,  a  marked  simplification. 

2.  During  the  latter  half  of  the  adult  ages  of  the  earth, 
there  seems  to  have  been  a  tendency  to  concentrate 
diastrophism  in  two  great  deformative  tracts  so  crossing 
one  another  as  to  relieve,  in  large  part,  the  greater 
stresses  that  arose  in  the  earth-body — a  tendency  to 
reduce  tripartition  to  bipartition,   as  the  earth  grew 
old  and  stiff.    These  two  great  belts,  in  the  latest  geologic 
ages,    were    "the    great    world-ridge" — the    American 
Cordilleras  projected  across  Asia  and  into  Africa — and 
the  great  Alps-Himalaya  mountain  tract.     Even  in  the 


214  THE  ORIGIN  OF  THE  EARTH 

development  of  these,  however,  there  appears  a  marked 
tendency  to  take  advantage  of  the  yield-tracts  previ- 
ously defined  by  the  basal  segmentation.  The  frame- 
work lines  were  followed  by  "the  world-ridge"  through 
South  America,  Central  America,  and  half  through  North 
America;  there  was  then  a  "cut-off"  to  the  Asian  tract, 
but  in  the  less  pronounced  extension  across  Arabia  and 
Africa,  the  basal  yield- tract  was  again  approximately 
followed.  The  transverse  Alpine-Himalayan  tract  also 
followed  the  basal  yield-tracts  in  Australia  and  East 
Asia,  but  in  its  westward  extension  across  the  Eur- 
african  segment  it  followed  the  fulcrum  zone.  In  other 
regions  this  zone — the  junction  line  between  the  recipro- 
cating triangular  segments,  the  fundamental  units  of 
the  whole  scheme — shows  signs  of  susceptibility  to  dis- 
ruption, but  that  cannot  be  dwelt  upon  here.  It  is 
merely  possible  to  emphasize  briefly  the  fundamental 
tendency  toward  simplification,  as  is  appropriate  in  a 
rigid  globe,  growing  more  and  more  rigid,  no  doubt,  as 
age  creeps  on. 

But  perhaps  the  most  singular  and  significant  of  all 
such  features  of  the  earth's  surface  is  the  alternate,  or 
offset,'  positions  of  the  northern  factors  relative  to  the 
southern,  as  the  offset  to  the  northwest  of  the  North 
Atlantic  relative  to  the  South  Atlantic,  of  North  America 
relative  to  South  America,  of  the  North  Pacific  relative 
to  the  South  Pacific,  and  of  Asia  relative  to  Australasia. 
The  offset  of  Europe  and  North  Africa  relative  to 
South  Africa  is  much  less  pronounced,  and  falls  in  with 
the  general  suggestion  of  appression  already  noted. 
This  prevailing  alternation  of  position  is  closely  in 
accord  with  its  assigned  origin  in  the  dovetail  arrange- 


THE  JUVENILE  SHAPING  OF  THE  EARTH      215 

ment  of  the  working  segmental  pairs  that  constituted 
the  assigned  primary  segmentation. 

EVOLUTION  OF  THE  SUB-OCEANIC  CONES 

Although  it  is  natural  to  give  first  attention  to  the  pro- 
truding elements  of  the  earth's  anatomy,  as  we  have 
done,  they  are  not  its  dominant  features;  they  are  really 
its  weak  features,  its  yield-effects.  The  master-features 
are  the  denser,  heavier,  stiffer,  depressed  centers  of  the 
segments  themselves.  Because  the  borders  were  dis- 
rupted and  protruded,  and  came  in  consequence  to  be 
the  tracts  of  lesser  specific  gravity,  as  already  set  forth, 
the  waters  gathered  progressively  toward  the  centers 
of  the  segments.  If  it  were  safe  to  follow  strictly  the 
analogy  of  the  basaltic  segments,  we  might  assume  that 
the  borders,  and  particularly  the  angles,  of  the  original 
six  quadrilateral  segments  were  elevated  while  the  centers 
were  depressed.  Probably  this  was  so,  but  without 
trusting  too  much  to  this,  the  dynamics  of  the  case  led 
to  central  depression  as  growth  went  on — and  to  some 
interesting  migrations  of  these  depressions  as  well.  We 
have  assigned  reasons  for  the  concentration  of  the 
heavier  material  in  the  centers  of  the  oceanic  basins. 
As  the  oceanic  waters  gathered,  they  lent  their 
weight  to  the  further  depression  of  the  abysmal  basins. 
Though  more  or  less  angular  in  coastal  details— 
the  effects  of  minor  agencies — these  basins  appear 
to  have  grown  in  general  circularity  as  the  natural 
result  of  the  erosions  and  depositions  of  the  gyrating 
oceanic  currents.  In  the  accompanying  figures  ovals 
have  been  drawn  to  emphasize  this  general  circularity 
(Figs.  30-38). 


216  THE  ORIGIN  OF  THE  EARTH 

By  the  progressive  concentration  of  the  heavier 
material  in  them  and  upon  them,  in  the  ways  already 
set  forth,  the  sub-oceanic  segments  were  subjected 
to  greater  vertical  pressure  than  the  land  segments  at  all 


FIG.  36. — View  of  the  Indian  Ocean,  showing  its  fundamental  cir- 
cularity, shown  by  the  oval,  and  the  main  yield-tracts  adjacent  to  it, 
indicated  by  the  straight  lines  which  define  the  quadrilateral  within 
which  the  ocean  lies. 

times  during  the  long  era  of  their  growth  and  even 
subsequent  to  their  appreciable  growth.  There  was 
periodic  yielding  to  this  in  the  interest  of  equilibrium  of 
stress,  and  this  involved  lateral  pressure  in  addition  to 


THE  JUVENILE  SHAPING  OF  THE  EARTH      217 

the  vertical  pressure.  Under  the  law  that  equal  pres- 
sure in  all  directions  increases  rigidity,  the  sub-oceanic 
segments  should  have  acquired  degrees  of  rigidity 
superior  to  those  attained  by  the  continental  segments, 
which,  as  the  yield-segments,  suffered  more  from 
differential  stresses.  The  sub-oceanic  segments  enjoyed 
some  advantages  of  attitude  and,  on  account  of  this, 
suffered  less  surface  deformation,  and  probably  less 
internal  distortion  also,  and  for  these  reasons  they  should 
have  been  less  affected  by  schistosity  and  the  allied 
adaptations  to  easement  movements. 

In  so  far  as  the  sub-oceanic  segments  came  to  have 
rounded  outlines  at  the  surface,  their  downward  exten- 
sions would  come  to  be  conical  rather  than  pyramidal. 
To  this  extent,  it  is  fitting  to  speak  of  them  as  cones. 
Whether  they  are  to  be  regarded  as  frustums  of  cones, 
reaching  merely  to  the  horizon  at  which  planetesimal 
growth  began,  or  as  complete  cones,  developed  to  the 
earth's  center  by  superior  pressure  and  by  dominance  in 
dias trophic  action,  we  need  not  turn  aside  here  to  con- 
sider. Whether  frustums  or  completed  cones,  they 
became  the  master-factors  in  the  shaping  of  the  earth 
by  reason  of  their  superior  specific  gravities,  their 
superior  rigidities,  their  relative  freedom  from  yielding 
tracts,  as  well  as  their  progressive  loading  which  served 
constantly  to  keep  them  under  growing  pressure. 

Five  of  the  ideal  six  oceanic  basins  attained  pro-  v 
nounced  development,  the  North  Atlantic,  the  South 
Atlantic,  the  Indian,  the  North  Pacific,  and  the  South 
Pacific.  Under  these  let  us  picture  five  great,  heavy, 
stiff,  sub-oceanic  cones.  What  should  have  been  the 
sixth,  in  an  ideal  development,  is  represented  by  the 


218  THE  ORIGIN  OF  THE  EARTH 

broken,  pitted  Caspian-Mediterranean  group  of  basins, 
with  its  strange  assemblage  of  abrupt  depressions  and 
elevations,  not  to  speak  of  the  strangely  elongate  fossae 
in  which  lie  the  Red  Sea,  the  Dead  Sea,  and  the  Adriatic 
(see  Fig.  33).  This  remarkable  combination  may  per- 
haps be  regarded  as  a  substitute  for  the  ocean  that 
ideally  should  have  had  a  place  in  the  heart  of  the  Eur- 
african  quadrilateral.  This  abortive  result  seems  to 
find  a  correlative  in  the  half-developed  Australasian 
continent  on  the  opposite  side  of  the  globe.  In  the 
earlier  geologic  ages  the  quasi-oceanic  mediterranean 
cluster  of  basins  embraced  wider  and  deeper  depressions 
than  now,  but  it  does  not  appear  ever  to  have  been 
merged  in  a  continuous  abysmal  basin,  at  least  not  in 
known  geologic  history. 

The  basins  destined  to  become  truly  abysmal  were 
probably  unequal  in  area  and  depth  at  the  start,  for 
inequalities  would  almost  inevitably  arise  in  the  primary 
segmentation  of  such  a  body  as  the  earth  yielding  under 
such  a  complex  of  stresses  as  were  brought  to  bear  upon 
it.  Such  inequalities  as  arose  at  the  outset,  or  in  the 
early  stages,  naturally  influenced  the  adjustments  of 
the  segments  to  one  another  in  the  later  stages,  and  so 
led  to  progressive  encroachments  of  the  greater  on  the 
lesser,  and  these  primitive  inequalities  grew,  in  time,  into 
the  still  larger  inequalities  of  today.  The  results  of  the 
struggle  between  these  factors  of  different  powers 
claim  a  moment's  attention. 

A  very  natural  effect  seems  to  have  been  the  pairing  of 
the  weak  with  the  strong  in  antipodal  positions.  The 
heavy,  relatively  rigid,  sub-oceanic  cones  stand  oppo- 
site the  lighter,  weaker,  yielding  continents.  The 


,       THE  JUVENILE  SHAPING  OF  THE  EARTH     219 

heavy  rigid  factors  came  also  to  be  larger  than  the  lighter 
weaker  ones,  in  about  the  ratio  of  two  to  one,  surface 
measure.  The  embossment  'of  North  America  lies 
opposite  the  basin  of  the  Indian  Ocean;  the  embossment 


FIG.  37. — South  Pacific  view  of  the  globe  and  the  adjacent  yield- 
tracts  on  the  east,  south,  and  west,  and  its  coalescence  with  the  North 
Pacific,  indicated  by  the  overlapping  of  the  circles,  which  define  the 
fundamental  circularity  of  the  oceans. 

of  Australia  lies  opposite  the  basin  of  the  North  Atlantic ; 
the  great  protuberance  of  Africa  is  antipodal  to  the 
abysmal  depths  of  the  Central  Pacific;  the  greater 
mass  of  Asia  is  antipodal  to  the  South  Pacific,  while 


220  THE  ORIGIN  OF  THE  EARTH 

its  eastern  extremity  lies  opposite  the  South  Atlantic 
basin;  South  America  is  antipodal  to  the  westward 
extension  of  the  North  Pacific.  The  equatorial  part  of 
the  South  Atlantic  basin  is  not  represented  by  an  anti- 
podal protrusion,  though  its  southern  part  lies  opposite 
the  Alaska-Siberian  bridge.  Thus  the  law  of  opposites, 
as  respects  both  position  and  dynamic  power,  is  well 
sustained,  though  not  perfectly  realized.  The  heavy, 
rigid,  sub-oceanic  masses,  with  their  superior  tendency 
to  work  toward  the  earth's  center,  are  rather  definitely 
correlated  with  the  lighter,  weaker  continental  masses 
that  have  shown  a  yielding,  protuberant  tendency 
throughout  geological  history. 

If  all  def ormative  actions  are  pictured  as  due  to  mere 
local  or  regional  surface  pressure  acting  on  a  viscous  or 
plastic  earth-body,  some  very  debatable  questions  as 
to  the  transmission  of  stresses  to  the  opposite  side  of 
earth  naturally  arise;  but  if  the  rotational,  the  tidal, 
and  the  larger  stress-effects  of  loading  and  unloading 
are  pictured  as  stress-differences  affecting  every  part  of 
the  body  and  the  central  portions  in  highest  degree,  and 
if  these  stresses  are  conceived  as  acting  preponderantly 
through  the  relatively  rigid  sub-oceanic  cones,  the  stiff er 
set  of  factors,  while  the  weaker  set  of  factors  opposed 
to  them  are  rendered  susceptible  of  yielding  by  zones 
of  schistosity,  the  struggle  for  advantage  of  position 
takes  on  a  different  aspect;  it  becomes  chiefly  a 
simple  contest  of  mechanical  push  and  yield  that 
reaches  its  climax  in  the  deep  interior.  The  stiff 
heavy  cones  naturally  should  have  found  accommoda- 
tion by  pressing  into  the  yielding  tracts  opposite  them. 
An  alternate  adjustment  with  the  opposing  cones  of 


THE  JUVENILE  SHAPING  OF  THE  EARTH     221 

their  own  stiff  type  may  be  regarded  as  a  necessary 
incident. 

An  inevitable  result  of  every  stage  of  progress  of  the 
heavy,  rigid,  sub-oceanic  cones  in  working  toward  the 
earth's  center  was  a  lateral  crowding  of  the  weaker, 
lighter,  continental  wedges  that  filled  the  space  between 
them.  The  observed  secular  tendency  to  up-yielding,  on 
the  part  of  the  continents,  as  the  reciprocal  to  the 
observed  oceanic  tendency  to  work  downward,  con- 
jointly with  the  inevitable  lateral  thrust,  thus  appears 
as  a  logical  consequence  of  the  whole  process  of  growth 
and  adjustment.  The  struggle  is  interpreted  as  but  a, 
method  of  seeking  isostatic  adjustment  in  a  form  not 
only  wholly  consistent  with  the  earth's  essential  rigidity, 
but  actuated  and  controlled  by  the  superior  rigidity  of  the 
sub-oceanic  cones. 

These  aggressive  actions  of  the  stronger  at  the  expense 
of  the  weaker  were  expressions  of  the  law  of  dominance, 
while  at  the  same  time  they  came  to  be  illustrations  of  the 
law  of  oppo sites,  and  of  the  law  of  alternates.  The  stiff 
heavy  cones  should  naturally  have  grown  more  and 
more  dominant  as  their  masses  and  their  rigidities 
increased,  and  as  their  competitors  suffered  in  resisting 
power  by  yielding  and  suffered  at  the  same  time  in 
weight  by  erosion  at  their  surfaces. 

Naturally  enough,  a  dominance  of  the  greater  sub- 
oceanic  cones  over  the  lesser  of  their  own  class  appears. 
The  three  greatest  sub-oceanic  cones — the  great  tri- 
umvirate that  lay  beneath  the  South  Pacific,  the  North 
Pacific,  and  the  Indian  oceans,  respectively — not  only 
appear  to  have  mastered  and  crowded  aside  their  lesser 
competitors  but  to  have  joined  forces  in  pushing  toward 


222  THE  ORIGIN  OF  THE  EARTH 

the  earth's  center.  In  so  doing  they  seem  not  only  to 
have  drawn  a  superior  measure  of  the  hydrosphere  and 
of  its  dissolved  rock  in  upon  themselves,  resulting  in  the 
well-recognized  water-hemisphere,  but  to  have  forced 


FIG.  38. — North  Pacific  view  of  the  globe,  showing  the  relations  of 
the  abysmal  basin  to  North  America,  Asia,  and  Australasia,  to  the 
Alaska-Siberian  bridge,  and  to  the  South  Pacific. 

the  weaker  cones  beneath  the  two  Atlantics,  and  the  con- 
tinental wedges  that  clustered  about  them  to  yield,  and 
by  such  yielding  to  have  formed  the  land  hemisphere. 
A  bilateral  asymmetry  was  thus  imposed  on  the  earth. 
Some  measure  of  this  might  indeed  be  accomplished  by 


THE  JUVENILE  SHAPING  OF  THE  EARTH     223 

a  shift  in  the  center  of  gravity  of  the  earth,  without 
diastrophism,  but  the  latter  seems  to  us  inevitable  also. 

We  have  spoken  of  the  Southern  Hemisphere  as 
dominant  in  specific  gravity,  in  subsidence,  in  water- 
accumulation,  in  lower  temperature,  and  in  heavier 
atmosphere;  but,  more  accurately  speaking,  the  center 
of  dominance  in  most  of  these  respects  lies  near  the 
junction  of  the  three  great  oceans;  causally  it  is  to  be 
referred  to  the  heavy  cones  that  lie  beneath  them.  The 
hemisphere  of  preponderant  gravity,  and  hence  of 
abysmal  areas  and  of  water  bodies,  centers  not  far 
from  New  Zealand,  while  the  compensatory  protuber- 
ances are  distributed  about  some  point  in  Southeastern 
Europe,  a  region  of  notable  instability,  of  tortuous 
folding,  of  pronounced  overthrusts,  upthrows,  and 
downthrows,  and  of  igneous  and  seismic  phenomena. 
There  may  be  no  causal  relationship  in  this,  but  it  is 
suggestive.  This  largest  of  deformative  concepts,  that 
of  hemispherical  adjustments,  compensations,  and 
balancings,  involves  extremely  massive  movements,  but 
perhaps  they  may  all  be  realized  by  the  wedging  action 
of  essentially  rigid  elements  separated  by  schistose 
tracts;  if  so,  in  their  combination  they  would  form  an 
essentially  rigid  earth. 

In  thus  carrying  forward  into  the  interpretation  of 
the  later  physiographic  configurations  some  rather  re- 
mote deductions  drawn  from  the  planetesimal  dynamics 
engaged  in  the  shaping  of  the  juvenile  earth,  we  are 
painfully  conscious  of  the  high  probability  that  we 
have  fallen  into  some  misconceptions,  perhaps  not  a 
few,  and  have  entertained  views  that  will  need  to  be 
rectified.  But  even  misconceptions  may  be  suggestive; 


224  THE  ORIGIN  OF  THE  EARTH 

they  are  likely  to  be  more  suggestive  than  no  conceptions 
at  all.  The  strong  trend  of  evidence,  converging  from 
several  quarters,  pointing  almost  unequivocally  to  a 
pervasively  rigid  earth,  lends  some  degree  of  sanction  to 
almost  any  serious  attempt  to  build  up  a  system  of 
dynamic  concepts  that  are  consistently  loyal  to  the 
known  behavior  of  crystallizing  rock-masses,  as  such, 
and  that  scrupulously  leaves  them  in  the  full  possession 
of  their  typical  qualities  at  all  stages  of  the  earth's 
reshaping. 

REFERENCES 

1.  E.  W.  Brown,  Address  on  Cosmical  Physics,  Brit.  Assn.  Adv.  Sci. 
Report,  Australia  (September,  1914),  pp.  311-21. 

2.  Sir  Joseph  Larmor,  "The  Influence  of  Local  Atmospheric  Cool- 
ing on  Astronomical  Refraction,"  Monthly  Notices  Roy.  Astron.  Soc. 
LXXV  (1915),  205-10;   "On  Irregularities  in  the  Earth's  Rotation,  in 
Relation  to  the  Outstanding  Discrepancies  in  the  Orbital  Motion  of  the 
Moon,"  ibid.,  pp.  211-19. 

3.  H.  Glauert,  "The  Rotation  of  the  Earth,"  Monthly  Notices  Roy. 
Astron.  Soc.,  LXXV  (1915),  489-95. 

4.  A.  A.  Michelson,  "Preliminary  Results  of  Measurements  of  the 
Rigidity  of  the  Earth,"  Astrophys.  Jour.  XXXIX  (1914),  105-38;  also 
Jour.  GeoL,  XXII  (1914),  97-130. 

5.  H.  G.  Gale,  "On  the  Experimental  Determination  of  the  Earth's 
Elastic  Properties,"  Science,  XXXIX  (1914),  927-33. 

6.  G.  H.  Darwin,  "On  the  Stresses  Caused  in  the  Interior  of  the 
Earth  by  the  Weight  of  Continents  and  Mountains,"  Phil.  Trans.  Roy. 
Soc.,  Pt.  I  (1882),  pp.  187-230. 

7.  F.  D.  Adams,  "The  Flow  of  Marble,"  Amer.  Jour.  Sci.,  XXIX 
(1910),  465-87;    "The  Depth  of  the  Zone  of  Flow,"  Jour.  GeoL,  XX 
(1912),   97-118;     "Differential   Pressures   in   Rocks   and   Minerals," 
Jour.  GeoL,  XVIII  (1910),  489-525;  Nature  (July,  1907),  p.  269. 

8.  P.  W.  Bridgman    "The  Measurement  of  Hydrostatic  Pressures 
up  to  20,000  Kilograms  per  Square  Centimeter,"  Proc.  Am.  Acad.  Arts 
and  Sciences,  XL VII  (1911),  No.  n,  pp.  321-43;  "Water,  in  the  Liquid 
and  Five  Solid  States,"  ibid.  (1912),  No.  13,  pp.  441-558;   "The  Col- 
lapse of  Thick  Cylinders  under  High  Hydrostatic  Pressure,"  Phys.  Rev., 
XXXIV  (1912),  No.  i,  pp.  1-24;  " Thermodynamic  Properties  of  Twelve 


THE  JUVENILE  SHAPING  OF  THE  EARTH      225 

Liquids  between  20°  and  80°  and  up  to  12,000  Kgm.  per  Sq.  Cm.," 
Proc.  Am.  Acad.  Arts  and  Sciences,  XLIX  (1914),  i;  "The  Technique 
of  High  Pressure  Experimenting,"  ibid.,  pp.  625,  654;  "Phase  Changes 
under  Pressure,  I,  The  Phase  Diagram  of  Eleven  Substances  with  Espe- 
cial Reference  to  the  Melting  Curve,"  ibid.,  p.  648;  "Polymorphic 
Transformations  of  Solids  under  Pressure,"  ibid.,  LI  (1915),  53-124. 

9.  F.  Becke,  "Ueber  Mineralbestund  und  Struktur  de  kristallinis- 
chen  Schiefer,"  Compt.  rend.    IX.  Cong.  Geol.  Internal.,  Vienna  (1903), 

PP-  555  f- 

10.  C.  R.  Van  Hise,  "A  Treatise  on  Metamorphism,"  Monogr.  47, 
U.S.  Geol.  Survey  (1904),  p.  182. 

n.  U.  Grubenmann,  Die  kristallen  Schiefer,  Part  I  (1904);  Part  II 
(1907). 

12.  C.  K.  Leith,  "Rock  Cleavage,"  Bull.  239,  U.S.  Geol.  Survey 
(1905),  pp.  23-118;  Structural  Geology  (1913),  pp.  76-93;  Metamorphic 
Geology  (with  W.  J.  Mead)  (1915),  pp.  169-93. 

13.  G.  F.  Becker,  "Finite  Homogeneous  Strain,  Flow  and  Rupture 
of  Rocks,"  Amer.  Jour.  Sci.,  IV  (1893),  14-90. 

14.  John  Johnston,  "Pressure   as   a   Factor  in   the  Formation  of 
Rocks  and  Minerals,"  Jour.  Geol.,  XXIII  (1915),  730-47. 


CHAPTER  IX 
INNER  REORGANIZATION  OF  THE  JUVENILE  EARTH 

The  heterogeneous  way  in  which  the  accessions  from 
the  parent  nebula  were  gathered  into  the  growing  earth, 
their  intermixture  with  air  and  water,  their  partial 
oxidation,  carbonation,  and  hydration,  and  their  pro- 
gressive burial  deeper  and  deeper  as  growth  proceeded, 
were  eminently  fitted  to  call  into  action  a  series  of 
readjustments,  recombinations,  and  recrystallizations 
in  the  interest  of  a  better  accommodation  to  the  new 
conditions  that  gradually  arose  in  the  interior.  Not 
only  was  each  layer  pressed  by  the  layers  that  accumu- 
lated above  it,  but  the  force  of  gravity  grew  with  each 
accession  and  the  growing  body  pulled  itself  together 
with  increasing  power  as  time  went  on.  The  total 
shrinkage  of  the  loose  surface  matter  in  reaching  its 
final  compact  form  was  nearly  a  third  of  its  original 
volume.  A  portion  of  the  energy  that  had  been  engaged 
in  maintaining  the  volume  of  the  mass  was  turned  by 
compression  into  heat  and  this  powerful  agency  for  both 
chemical  and  physical  change  was  brought  into  action. 
At  the  same  time  and  by  the  same  act,  growing  pressure 
was  brought  to  bear,  the  normal  effect  of  which  is 
increase  of  rigidity.  There  thus  arose  in  the  interior  a 
contest  of  co-operative  but  yet  antagonistic  agencies,  a 
contest  not  unlike  that  waged  by  the  geologic  triumvirate 
on  the  surface. 

226 


REORGANIZATION  OF  THE  JUVENILE  EARTH      227 
THE  RADIOACTIVE  FACTOR 

There  was  here  also  a  third  agency,  atomic  dissocia- 
tion. Radioactive  elements  in  undergoing  spontaneous 
decomposition,  then  as  now,  no  doubt  shot  streams 
of  electrons  and  alpha-particles  into  the  adjacent  matter 
at  such  prodigious  velocities  that  they  penetrated  to 
appreciable  distances  and  constantly  tended  to  raise  the 
temperature.  Radioactive  heat  was  thus  added  to  the 
heat  of  compression.  It  is  assumed  that  the  radioactive 
elements  came  in  with  the  other  accessions  from  without 
and  that  they  were  scattered  at  random  through  the 
successive  layers  added  to  the  earth.  Special  students 
of  the  subject  find  by  computation  that,  if  radioactive 
matter  were  scattered  through  the  interior  uniformly 
with  a  value  equal  to  that  in  the  surface  rocks,  a  layer  less 
than  forty  miles  in  depth  would  generate  as  much  heat 
as  the  earth  is  now  giving  forth.  There  is  no  experi- 
mental evidence  that  such  degrees  of  heat  and  pressure 
as  prevail  in  the  earth  would  restrain  the  disintegrating 
habits  of  radioactive  matter  and  explain  on  this  basis 
the  relatively  low  measure  of  heat  arising  from  the 
interior.  It  is  therefore  inferred  that  the  radioactive 
material  was  originally  scattered  sparsely  through  the 
whole  ingathered  mass  but  was  concentrated  later  at  the 
surface.  This  is  quite  in  harmony  with  the  evidence 
gathered  from  fresh  effusions  of  lava  presumed  to  come 
from  considerable  depths,  from  meteorites  that  come 
from  space,  from  the  sun  and  the  stars,  which  implies 
scantiness  rather  than  richness  in  radioactive  elements. 
It  is  therefore  assumed  that  there  was  only  a  sparse 
distribution  of  radioactive  elements  in  the  parent  nebula, 
and  hence  in  the  original  material  of  the  earth,  but 


228  THE  ORIGIN  OF  THE  EARTH 

that  there  was  progressive  concentration  of  these  at  the 
surface  as  effusive  igneous  action  went  on. 

This  revolutionary  factor  was  quite  unknown  and 
unanticipated  when  the  planetesimal  view  of  earth- 
problems  was  first  entertained,  and  it  is  interesting  as 
well  as  gratifying  to  see  how  happily  it  falls  in  with  the 
processes  already  postulated.  The  new  factor  is  to 
be  pictured  as  giving  rise  to  a  multitude  of  minute  self- 
heating  centers  scattered  at  random  through  the  growing 
mass  and  adding  sharply  localized  heat  to  that  which 
arose  more  uniformly  from  compression. 

STRESS   CONTROL  OF  THE   INTERIOR 

Let  us  not  fail  to  note,  at  the  outset,  the  stress- 
conditions,  for  they  are  held  to  be  a  vital  agency  in 
forcing  liquid  matter  to  the  surface  as  fast  as  formed 
in  workable  quantities,  except  as  its  specific  gravity 
may  have  been  high  enough  to  resist  this.  Besides 
the  simple  hydrostatic  pressure  of  gravity,  equal 
in  all  directions,  there  were  stress-differences  arising 
from  changes  of  rate  of  rotation,  from  the  pulses  of 
the  body  tides,  and  from  shrinkage.  Let  us  accept 
the  modern  view  that  equal  pressure  in  all  directions 
tends  toward  rigidity,  while  unequal  pressures,  or  stress- 
differences,  favor  solution,  fusion,  recrystallization,  and 
like  changes.  The  gravitative  pressures — which  now 
range  from  one  atmosphere  at  the  surface  to  about 
three  million  atmospheres  at  the  earth's  center — were 
indeed  less  than  this  while  the  earth  was  in  its  juvenile 
stages,  but  proportionally  less  force  was  required  to 
expel  liquids  then.  The  special  nature  and  the  high 
competency  of  the  rotational  stress-differences  have 


REORGANIZATION  OF  THE  JUVENILE  EARTH      229 

already  been  emphasized.  The  tidal  stress-differences 
were  small  and  no  doubt  always  fell  within  the  elastic 
limits  of  rock  except  when  very  close  to  the  yield-point 
from  other  causes;  none  the  less,  a  perpetual  alternation 
of  even  minute  stresses  and  reliefs,  acting  on  rocks  whose 
temperatures  were  rising  and  whose  molecules  were 
approaching  the  critical  point  of  loosening  their  holds, 
was  quite  certain  to  accelerate  such  loosening  by  adding 
the  critical  amount  of  stress  needed. 

Without  doubt,  the  most  important  feature  of  the 
tidal  and  the  rotational  stress-differences  in  this  con- 
nection lay  in  the  vital  fact,  already  repeatedly  empha- 
sized, that  they  were  greatest  at  the  center  and  graduated 
outward.  Their  action  was  not  unlike  a  vise  closing 
from  below.  They  were  superposed  on  the  hydrostatic 
stresses  of  gravity  which  graded  still  more  strongly  from 
the  center  outward,  and  which,  though  pressing  equally 
in  all  directions  at  any  given  point,  yet  had  a  selective 
effect  which  of  itself  tended  to  force  the  lighter  liquids  to 
the  surface.  The  nature  and  distribution  of  the  stresses 
that  arose  from  shrinkage  and  other  sources  were  too 
complicated  to  be  discussed  in  this  connection.  It 
may  merely  be  noted  that  all  the  lands  were  suffering  loss 
of  weight,  at  least  relatively,  and  that  all  the  oceans 
were  gaining  load.  When  it  is  considered  that  the 
mechanical  sediments  were  chiefly  gathered  in  shelves 
about  the  borders  of  the  lands  and  that  they  thus  formed 
a  network  enveloping  the  earth,  and  when  it  is  further 
considered  that  the  material  dissolved  from  the  lands 
was  diffused  through  the  oceans,  increasing  their  weight, 
and  that  they  enveloped  the  earth  in  a  belt  of  broad 
areas,  it  can  scarcely  be  questioned  that  these  two 


230  THE  ORIGIN  OF  THE  EARTH 

comprehensive  systems  of  loading  the  earth  generated 
widely  prevalent  and  deep  stress-differences,  and  that 
their  general  effects  on  mobile  matter  within  the  earth 
must  have  been  analogous  to  those  of  the  rotational  and 
tidal  stresses. 

Taken  conjointly,  these  seem  amply  to  warrant  the 
view  that  the  earth-body  was  at  frequent  intervals, 
if  not  more  or  less  constantly,  permeated  by  stress- 
differences  whose  tendencies  were  to  force  to  the  surface 
all  mobile  material  whose  specific  gravities  were  insuffi- 
cient to  resist  them.  This  was  a  mechanism  well  suited 
to  preserve  the  solidity  of  the  earth  against  increasing  heat 
and  growing  liquefaction  by  forcing  the  heat-product 
and  a  vital  portion  of  the  heat  itself  to  the  surface. 

The  precise  mode  by  which  lavas  find  their  way 
through  solid  continuous  rock,  such  as  prevails  below 
the  zone  of  fracture,  is  a  problem  not  yet  fully  elucidated. 
That  they  do  penetrate  such  rock  seems  to  be  placed 
beyond  question  by  the  hundreds  of  volcanic  vents 
that  must  apparently  connect  with  the  heated  regions 
that  lie  much  below  the  zone  of  fracture.  The  fact  that 
igneous  effusions  avail  themselves  of  fissures  in  the  zone 
of  fracture  does  not  answer  the  question  of  their  mode 
of  penetrating  the  unfissured  zone  below.  The  upper 
part  of  this  zone  of  continuous  rock  seems  clearly  to  have 
a  much  lower  temperature  than  molten  lavas  and  so  has 
a  chilling  effect  on  them  which  is  an  adverse  factor. 
So,  too,  the  stresses  thus  near  the  surface  are  generally 
of  the  lower  order,  except  at  times  of  diastrophism. 
These  factors  make  the  present-day  problem  quite  as 
insistent  as  that  of  the  earlier  ages  and  of  the  deeper 
horizons.  The  process  of  penetrating  the  cold  crust 


REORGANIZATION  OF  THE  JUVENILE  EARTH      231 

would  seem  to  be  somewhat  more  difficult  than  that 
of  lower  horizons  where  the  temperatures  are  higher 
and  where  the  liquefaction-curve  is  probably  nearer 
the  temperature-curve.  As  lavas  have  been  poured 
forth  at  all  known  geologic  ages  and  at  a  multitude 
of  points  on  the  earth's  surface,  there  seems  no  need 
to  regard  the  possibility  of  escape  of  lavas  as  a  special 
question  affecting  our  problem.  The  fact  that  the  earth 
is  now  giving  forth  lavas  at  many  points,  at  intervals 
and  in  little  driblets,  though  the  earth  is  certainly  now 
essentially  solid  and. even  highly  rigid,  is  interpreted  as 
a  living  expression  of  the  view  here  urged,  to  wit :  that  the 
mechanical  stresses  within  the  earth  force  lavas  out 
essentially  as  soon  as  they  accumulate  to  working  vol- 
umes. The  small  average  size  of  present  eruptions 
implies  that  the  quantity  of  lava  required  to  constitute 
such  working  volume  is  small.  In  harmony  with  this  is 
the  significant  fact  that  no  damping  effects  of  molten 
rocks  on  the  transmission  of  earthquake  waves,  nor 
on  the  elastic  response  of  the  earth-body  to  tidal  stress, 
have  been  detected.  Pronounced  tidal  movements 
might  be  expected  in  the  necks  of  volcanoes  if  they  were 
connected  with  large  reservoirs  of  lava  below,  but  if 
there  is  any  response  to  tidal  strains  at  all,  it  is  scarcely 
detectable.  The  independence  of  volcanoes  quite  near 
one  another  is  pointed  evidence  adverse  to  a  liquid 
connection  and  to  great  subterranean  reservoirs.  Nor 
is  this  mitigated  by  evidences  of  sympathy  of  a  certain 
sort,  when  under  the  same  stresses,  or  affected  by  the 
same  source  of  agitation. 

If  we  turn  for  a  moment  to  the  constructive  side  of 
the  problem,  the  process  of  rock-flow  by  recrystallization 


232  THE  ORIGIN  OF  THE  EARTH 

offers  suggestions  in  the  hints  it  gives  of  the  ability  of 
free  matter  to  move  through  solid  rocks  under  high 
pressure.  In  such  recrystallization  there  is  obviously 
not  a  little  movement  of  molecules  into  new  positions, 
else  old  crystals  could  not  take  new  shapes  and  align 
themselves  in  harmony  with  the  stresses  that  force  the 
reorganization;  much  less  could  new  crystals  form. 
In  most  of  the  cases  critically  studied  there  does  not 
seem  to  have  been  even  a  close  approach  to  general 
melting  or  solution,  but  only  a  very  partitive  molecular 
action. 

In  the  cases  we  most  wish  to  consider,  the  most 
soluble  portion  of  the  mass  is  assumed  to  have  passed 
into  the  liquid  state.  This,  in  itself,  helped  to  prepare 
the  way  for  the  movement  of  this  liquid  portion  by  at 
least  partially  preparing  liquid  passageways.  If  not 
at  once  adequate,  delay  would  increase  the  liquefaction 
and  lead  on  toward  adequacy,  so  that,  long  before  the 
whole  mass  became  liquid,  a  way  of  escape  would  be 
provided  by  the  process  itself.  It  is  helpful  to  observe 
that,  while  mean  pressures  may  be  the  same  on  liquid 
as  on  solid  rock,  the  pressures  on  the  liquid  are  trans- 
mitted equally  in  a\\  directions  and,  as  a  result,  the 
liquid  may  insinuate  itself  into  the  most  yielding  planes, 
or  into  the  weakest  points,  in  the  crystalline  mass;  on 
the  other  hand,  the  crystals  are  subject  to  unequal 
strain  and  to  the  development  of  weaknesses  between, 
or  within,  themselves,  of  which  the  liquid  may  take 
advantage. 

There  seems  good  warrant,  then,  in  observed  vulcan- 
ism  and  in  theoretical  considerations,  for  the  generaliza- 
tion that  molten  rock  is,  and  probably  always  has  been, 


REORGANIZATION  OF  THE  JUVENILE  EARTH      233 

persistently  squeezed  out  of  the  earth  by  the  stresses 
and  strains  that  permeate  it.  The  periodicity  of  these 
stresses  and  strains  gives  periodicity  to  vulcanism,  but 
the  limited  volume  of  liquid  matter  requisite  to  incite 
expulsion  seems  to  have  extended  vulcanism  beyond 
the  periods  of  marked  diastrophism  because  the  stress 
requirements  are  so  small. 

With  this  environment  of  stress  and  strain  and  its 
expulsory  tendency  ever  in  mind,  let  us  turn  to  the 
changes  which  the  heterogeneous  mixture  of  material 
in  the  interior  must  probably  have  undergone  as  the 
temperatures,  the  pressures,  and  the  stress-differences 
waxed  more  and  more  intense  with  progressive  burial. 
It  need  hardly  be  urged  that  there  would  be  pre- 
eminent opportunities  as  well  as  insistent  demands  for 
physical  readjustments,  for  chemical  recombinations, 
and  for  adaptive  recrystallizations.  There  would  be 
especial  urgency  toward  those  readjustments,  combi- 
nations, and  recrystallizations  that  brought  better 
adaptation  to  the  increasing  heat,  pressures,  and  stress- 
differences. 

DIVERGENT  COURSES   OF  HEAT 

The  part  played  by  heat  was  obviously  critical.  Let 
it  then  be  carefully  noted,  at  the  outset,  that  each 
increment  of  heat  was  likely  to  suffer  partition  into  three 
portions,  one  to  be  consumed  in  forming  new  heat- 
absorbing  solid  compounds,  another  to  produce  lique- 
faction of  the  most  soluble  or  fusible  rock  substance, 
taking  the  latent  form,  and  the  third  to  remain  as  sensible 
heat,  maintaining  the  new  temperature  status  of  both 
rock  and  liquid.  The  first  remained  as  energy  of  organi- 


234  THE  ORIGIN  OF  THE  EARTH 

zation.  The  second  went  with  the  liquid  wherever  the 
stresses  and  strains  forced  it,  mainly  upward  and  out- 
ward. The  third  followed  alternate  courses :  a  part  was 
carried  toward  the  surface  with  the  ascending  liquids  and 
later  radiated  into  space;  a  part  was  carried  toward  the 
surface  by  conduction;  and  a  part  remained  as  an  incre- 
ment of  temperature.  This  last  was  always  subject  to 
loss  by  conduction.  While  there  was  therefore  a  tendency 
to  increase  the  central  heat  and  steepen  the  temperature 
gradient,  so  long  as  compression  remained  efficient  and 
so  long  as  radioactive  particles  remained  in  effective 
abundance,  there  went  hand  in  hand  with  this  tendency 
to  increase  a  group  of  checking  processes.  The  probable 
result  was  an  equally  constant  tendency  toward  an 
equilibrium  in  which  the  chief  controlling  element  was 
the  solution  or  fusion  of  the  most  soluble  or  fusible 
compound  in  the  heterogeneous  mixture.  The  main 
action  was  probably  mutual  solution  rather  than 
melting.  It  is  not  known  that  simple  pressure,  by  the 
heat  it  generates,  will  melt  any  substance  that  shrinks 
on  crystallizing — which  includes  practically  all  under 
consideration — so  far  as  experimentation  covers  the 
case;  pressure,  on  the  contrary,  increases  the  rigidity 
of  all  such  substances.  It  was  probably,  therefore, 
chiefly  the  heat  of  radioactivity,  and  perhaps  certain 
chemical  reactions,  that  promoted  liquefaction.  The 
temperature  should  then  have  been  regulated  by  lique- 
faction and  probably  never  rose  above  the  solution- 
curve  of  the  most  soluble  substances  that  remained  at 
each  given  horizon.  The  thermal  gradient  and  the 
solution-curve  were  identical  throughout  the  liquefying 
horizons. 


REORGANIZATION  OF  THE  JUVENILE  EARTH      235 
SELECTIVE  LIQUEFACTION 

Now  it  is  important  to  observe  that  the  assigned  rise  of 
pressure  was  very  gradual  and  the  increment  of  heat 
arising  from  it  at  any  stage  was  very  deliberate.  So  also 
was  the  heat  generated  by  the  sparse  radioactive 
material.  So  probably  was  the  heat  from  all  other 
assignable  sources.  The  portion  available  for  lique- 
faction at  any  time,  in  spite  of  the  restraining  influence 
of  pressure,  and  over  and  above  the  part  carried  away 
by  conduction  and  liquid  extrusion,  and  the  part  con- 
sumed in  recombination  and  reorganization,  is  believed 
to  have  been  relatively  small  and  to  have  been  sufficient 
only  to  cause  the  solution  of  a  very  small  part  of  the 
whole  mass.  This  part,  of  course,  was  that  which  was 
most  soluble  under  the  existing  conditions.  The  selec- 
tion was  much  affected  by  the  particular  contacts  that 
happened  to  be  available  in  each  particular  spot.  The 
nature  of  the  contacts  was  obviously  a  vital  matter. 
The  principles  of  eu  tec  tics  should  have  found,  in  the 
intimate  mixture  of  the  accessional  material  and  in  the 
slowly  changing  conditions  of  the  interior,  a  supreme 
field  of  action. 

The  heat  arising  from  the  sparse  content  of  radioactive 
particles  was  limited  and  was  generated  gradually.  It 
was  also  undergoing  steady  removal.  The  radioactive 
molecules  themselves  had  high  specific  gravities,  but 
each  must  have  heated  by  its  projectiles  some  billions 
of  adjacent  molecules,  so  that  the  average  specific 
gravity  of  the  melt  or  the  solution  that  resulted  would 
differ  little  from  the  common  average  and  would  respond 
to  the  stresses  and  strains  imposed  on  the  common  mass  in 
about  the  normal  way,  save  that  the  higher  temperature 


236  THE  ORIGIN  OF  THE  EARTH 

which  the  radioactivity  would  continue  to  generate 
would  favor  buoyancy.  Even  in  the  little  viscous  mass 
generated,  the  part  close  about  the  heating  particle 
should  gain  a  superior  temperature  and  so  rise  to  the 
top  and  be  brought  to  bear  where  it  could  do  most  to 
bore  its  way  upward. 

One  of  the  first  effects  of  rising  temperature  on  the 
heterogeneous  accessional  mass  would  be  the  freeing 
of  the  atmospheric  and  hydrospheric  elements  that  had 
been  entrapped  with  the  accessions,  or  had  united  with 
them.  These  volatile  elements  should  enter  the  globules 
'of  liquid  rock  as  fast  as  they  were  formed,  should  lower 
their  specific  gravities,  and  should  increase  their  tendency 
to  ascend.  The  same  may  be  said  of  other  gaseous 
and  aqueous  matter  that  had  previously  entered  into 
combination  with  the  planetesimals  and  had  been  re- 
tained and  buried  with  them. 

It  appears  then  that  the  volatile  constituents,  the 
more  soluble  or  fusible  elements  and  the  self-heating 
particles,  should  have  formed  the  earliest  lavas.  These 
should  have  carried  to  the  surface  not  only  a  portion  of 
the  interior  heat,  but  a  portion  of  the  heat  generators. 
The  succeeding  liquefactions  should  have  involved 
the  next  most  soluble  or  fusible  constituents  and  should 
similarly  have  carried  out  a  part  of  the  residue  of  self- 
heating  matter.  And  so  the  selective  liquefying  action 
and  the  progressive  removal  of  the  radioactive  element 
should  have  proceeded  in  mutual  co-operation  toward 
a  predetermined  end. 

SELECTIVE   SOLIDIFICATION 

On  the  other  hand,  the  residue  should  have  increased 
in  average  refractoriness  by  this  selective  action  and  by 


REORGANIZATION  OF  THE  JUVENILE  EARTH      237 

the  recombinations  that  had  been  induced  in  the  interest 
of  stability.  At  the  same  time,  the  hydrostatic  pressure 
at  any  given  point  in  the  depths  was  undergoing  increase 
not  only  by  the  continued  accessions  to  the  surface, 
but  by  the  removal  of  liquefied  material  from  the  given 
horizon  to  a  superior  one,  perhaps  the  surface,  where 
its  weight  was  also  brought  to  bear. 

In  addition  to  these  increments,  the  compressibility 
was  quite  certainly  losing  effectiveness  under  the  general 
law  that  compressibility  declines  with  compression.  In 
addition  to  this,  the  refractory  residue  was  probably  less 
compressible  than  the  previous  mixed  mass.  Dr. 
Moulton  calls  attention  to  the  further  significant  fact 
that  the  potential  energy  set  free  as  the  center  is  ap- 
proached constantly  declines.  These  several  sources 
of  decline  in  the  effectiveness  of  compressibility  lessened 
the  heat  developed  from  that  source  at  any  given 
point  by  further  surface  weighting.  If  the  curve  of 
compressibility  is  asymptotic,  as  is  probable,  the  incre- 
ment of  heat  in  the  deeper  interior  would  tend  to  become 
negligible;  it  might  even  be  changed  to  a  decrement, 
for  conduction  might  be  able  first  to  equal  and  then  to 
surpass  it. 

The  selective  process,  by  the  removal  of  the  silicates 
in  larger  proportion  than  the  metals  and  metallic  alloys, 
probably  tended  to  concentrate  the  latter  toward  the 
center  and  to  make  them  ultimately  a  large  part  of  the 
residuum.  By  this,  the  conductivity  would  be  increased 
and  be  able  the  sooner  to  overmatch  the  small  increment 
of  heat  arising  from  the  vanishing  effectiveness  of 
compression. 

There  seem,  therefore,  to  be  excellent  grounds  for 
believing  that  the  selective  separation  of  the  inner 


238  THE  ORIGIN  OF  THE  EARTH 

substance  of  the  earth  into  a  liquid  ascensive  portion 
and  a  solid  residuum  growing  more  and  more  rigid  was  a 
definitely  declining  process  and  that  ultimately  a  nearly 
static  highly  rigid  state  was  reached. 

Precedence  has  been  given  to  selective  liquefaction  and 
the  effective  removal  surfaceward  of  the  most  solvent 
or  fusible  elements  in  the  originally  mixed  aggregate. 
It  was  noted  that  a  certain  portion  of  the  heat  developed 
should  have  promoted  endothermic  reactions  and  should 
thus  have  passed  into  structural  functions  and  dis- 
appeared as  heat.  It  remains  to  observe  more  broadly 
that  the  changes  in  heat,  in  pressure,  in  stresses  and 
strains,  together  with  the  selective  removals,  should 
have  been  highly  favorable  to  progressive  recombinations 
and  recrystallizations.  Under  the  influence  of  periodic 
stress-differences  superposed  on  graded  static  pressures, 
and  under  the  stimulus  of  rising  heat,  new  combinations 
and  new  crystallizations  of  the  solid  residue  should  have 
followed  one  another  until  the  best  accommodation  to 
the  existing  conditions  at  each  horizon  was  reached. 

The  inner  reorganization  of  the  juvenile  earth  is,  there- 
fore, pictured  as  a  process  that  affected  pervasively  the 
whole  interior  of  the  earth,  preserving  effectively  the  solid 
state  of  the  main  mass  and  progressively  increasing  its 
average  rigidity,  while,  at  the  same  time,  it  set  free  and 
forced  toward  the  surface,  stage  by  stage,  the  lighter  and  more 
mobile  material. 

It  was  previously  noted  that  the  inelastic  and  mag- 
netic material  had  probably  been  somewhat  concentrated 
in  the  heart  of  the  earth,  but  only  very  partially  so. 
The  processes  just  described  should  have  pushed  the 
concentration  to  much  greater  lengths  by  the  removal  of 


REORGANIZATION  OF  THE  JUVENILE  EARTH      239 

the  lighter  elements,  so  far  as  soluble  under  the  condi- 
tions developed,  and  by  differential  separation  in  the 
liquid  state,  so  far  as  that  obtained.  No  complete 
differentiation  is  postulated  even  as  the  ultimate  result. 
The  mixed  states  of  meteorites,  our  best  guide  in  the 
matter,  do  not  encourage  the  notion  of  complete  segre- 
gation. 

LIQUEFACTIVE  CONTROL  OF   TEMPERATURE 

If  the  preceding  sketch  of  inner  reorganization  is  in  the 
line  of  truth,  the  interior  heat  should  never  have  risen 
to  the  great  heights  that  have  often  been  assigned  it, 
for  the  heat  was  progressively  consumed  or  carried 
away.  The  process  was  long,  for  the  growth  was 
gradual;  much  of  the  material  came  to  the  surface, 
again  underwent  burial,  reheating,  and  reorganization; 
again  came  to  the  surface,  and  so  on;  the  heat  removal 
was  proportionate.  The  thermal  curve  of  the  interior 
should  have  been  determined  at  all  stages  automatically 
by  the  contesting  agencies,  and  should  have  been  coinci- 
dent with  the  curve  of  selective  solubility  for  that 
stage.  A  completely  liquid  state — much  less  a  central 
gaseous  state — are  held  to  be  incompatible  with  the 
mechanism  that  presided  over  the  building  of  the  earth. 
They  seem  to  be  equally  inconsistent  with  the  testi- 
mony of  seismic  waves  and  with  the  tidal  responses 
to  the  moon  and  the  sun.  The  preceding  sketch 
harmonizes  with  this  testimony  in  assigning  to  the  main 
body  of  the  earth,  if  not  to  its  whole  interior  mass,  an 
elastic  rigid  nature. 

The  function  of  igneous  effusions  in  the  economy  of 
the  earth  may  be  likened  to  the  function  of  perspiration 


240  THE  ORIGIN  OF  THE  EARTH 

in  the  economy  of  animals,  a  means  of  carrying  forth  to 
the  surface  and  discharging  the  excess  of  heat  and  of 
fluids  arising  from  the  inner  activities  of  the  organism. 
The  mutations  of  the  inner  earth  may  be  summarized 
as  a  single  prolonged  process  by  which  the  more  fluent, 
solvent,  and  lighter  material  of  the  earth-body  was 
concentrated  toward  the  surface,  while  the  more 
immobile,  refractory,  and  heavier  matter  was  concen- 
trated toward  the  center.  The  result  may  be  pictured  as 
a  central  core  dominated  by  metallic  alloys  and  a  thick 
enveloping  sphere  dominated  by  silicates.  The  whole  is 
regarded  as  essentially  crystalline,  the  crystallization  in 
the  depths  being  controlled  by  pressure  in  the  interest 
of  spatial  economy.  In  the  movement  tracts  parallel 
recrystallization  prevailed  and  a  schistose  structure 
followed.  The  arrangement  of  atoms  and  molecules 
in  the  heart  of  the  earth  was  probably  controlled  in  the 
main  in  the  interest  of  the  internal  fixation  of  energy 
and  was  predominantly  endo thermic.  In  contrast  to  this, 
the  matter  that  rose  to  the  surface  promoted  the  dis- 
persion of  energy.  It  is  probable  that  the  concentration 
of  the  metallic  elements  toward  the  center  contributed  to 
increasing  complexity  in  the  alloys  of  the  earth's  core. 
The  interpretation  of  the  deep-seated  deformative 
movements  and  of  the  transmission  of  seismic  waves 
through  the  central  region  should  probably  be  guided  by 
the  characteristics  of  alloys  rather  than  of  silicates. 


CHAPTER  X 

HIGHER   ORGANIZATION  IN  THE    GREAT   CONTACT 
HORIZONS 

The  contact  surfaces  between  earth,  air,  and  water 
are  the  sites  of  the  most  distinctive  geologic  activities  of 
the  present  day,  and  as  far  back  as  a  good  record  goes 
these  contact  zones  have  been  the  seats  of  the  most 
declared  denudations  and  depositions.  They  have  been 
almost  the  sole  habitats  of  biological  and  psychological 
activity.  The  initiation  of  terrestrial  life  and  the  dawn 
of  terrestrial  mentality  within  these  horizons  were  the 
last  radical  events  in  the  genesis  of  the  earth.  As 
sequences  of  the  nebulous  stages,  and  of  the  long  chain 
of  organizing  processes  we  have  tried  to  sketch,  these 
supreme  evolutions,  take  on  the  aspect  not  only  of  extraor- 
dinary physico-chemical  syntheses,  but  of  syntheses  with 
psychic  activities  whose  fundamental  nature  has  not 
yet  been  fully  compassed  by  determinate  science.  To 
any  who  may  prefer  to  regard  the  vital  and  mental  ele- 
ments as  supernatural  additions  to  the  physico-chemical 
factors,  the  combinations  must  still  seem  remarkable 
syntheses,  for  the  relationships  are  extremely  close 
and  the  interdependencies  singularly  complete.  From 
the  naturalistic  point  of  view,  these  climacteric  develop- 
ments embody  three  great  steps:  (i)  an  ascent  in  the 
complexity  of  physico-chemical  combination  until  it 
attained  the  organic  type,  (2)  an  evolution  of  physio- 
logical processes  and  of  organs  subservient  to  these, 
and  (3)  the  initiation  and  the  varied  deployment  of 

241 


242  THE  ORIGIN  OF  THE  EARTH 

psychological  phenomena.  These  seem  to  have  followed 
one  another  in  ascensive  order.  Their  close  sequences, 
in  a  common  habitat,  seem  to  imply  that  each  earlier 
step  was  prerequisite  to  each  later  advance,  and  that  the 
three  steps  form  a  single  genetic  series;  but  it  is  perhaps 
premature  to  affirm  this,  for  the  connecting  links,  as  yet, 
lack  complete  demonstration. 

QUASI-ORGANIC   SYNTHESES 

The  first  step  embraces  a  long  chain  of  complex 
physico-chemical  combinations  that  do  not  appear  to 
have  been  completed  either  above  or  below  these  contact 
surfaces,  or  in  the  heart  of  the  earth,  or  in  any  known 
region,  previous  to  the  earth's  adolescent  organization, 
but  of  course  it  cannot  be  said  that  they  were  previously 
absent  everywhere. 

The  type  of  synthesis  was  notable  in  being  selective 
rather  than  general.  The  outer  surface  of  the  earth- 
body  is  not  very  notably  synthetic,  on  the  whole,  either 
chemically  or  physically.  Technically,  it  is  the  zone 
of  &a/amorphism,  the  zone  of  downward  changes. 
Igneous  effusions  from  within  the  earth  commonly 
pass  by  weathering  into  simpler  combinations.  The 
silicates  that  form  by  far  the  larger  part  of  the  outer 
terranes  of  the  earth-body  are  rather  notably  prone  to 
disintegration  in  contact  with  air  and  water  and  to  take 
on  less  complex  forms.  Residual  earths,  in  particular, 
are  rather  marked  simplifications  of  the  silicate  com- 
pounds from  which  they  were  derived. 

Yet,  in  marked  contrast  to  this  katamorphic  tend- 
ency, there  arose  a  special  series  of  synthetic  actions 
that  led  the  way  to  types  of  organization  so  far  transcend- 


ORGANIZATION  IN  GREAT  CONTACT  HORIZONS     243 

ent  as  to  require  recognition  as  distinct  phases  of  earth- 
genesis,  indeed,  as  its  most  remarkable  phases.  The 
series  emerged  very  gradually,  it  would  appear,  from 
the  more  common  activities  that  had  previously  pre- 
vailed. The  action  centered  about  combinations  of 
carbon  with  the  constituents  of  the  atmosphere  and 
of  the  hydrosphere  to  which  were  added  special 
limited  selections  from  the  rock  constituents.  Solar 
and  other  energies  entered  into  the  synthesis  and 
were  perhaps  its  most  vital  element.  The  products  are 
conveniently  called  carbon  compounds.  It  is  the 
accepted  working  hypothesis  of  most  students  of  the 
subject  that  there  was  a  continuous  series  of  carbon 
compounds  leading  up  from  such  as  had  long  been  formed 
under  celestial  conditions  and  in  the  parent  nebula  and 
later  in  the  interior  of  the  earth,  and  in  the  air,  and  in  the 
waters,  until,  at  length,  they  reached  those  extremely 
complex  forms  that  constitute  the  bodies  of  livin'g 
beings.  Hypothetically,  the  whole  wide  gap  between 
the  simpler  carbon  compounds  and  the  most  intricate 
organic  compounds  was  thus  bridged.  But,  as  yet,  both 
observation  and  laboratory  research  fall  short  of  fully 
substantiating  this,  though  encouraging  advances  in 
building  up  such  a  connecting  series  are  being  con- 
tinually made. 

However  pronounced,  therefore,  our  theoretical  pre- 
possessions may  be,  and  however  confidently  we  may 
rest  on  the  doctrine  of  continuity  and  derivation,  it  must 
be  frankly  confessed  that  the  complete  graded  series 
of  postulated  synthetic  compounds  is  neither  observable 
in  nature,  nor,  as  yet,  producible  by  art.  Neither  the 
carbon  compounds  that  appear  to  have  arisen  in  the 


244  THE  ORIGIN  OF  THE  EARTH 

long  past  without  the  concurrence  of  life,  nor  those  that  can 
now  be  induced  by  manipulative  skill,  entirely  fulfil  evo- 
lutionary expectations.  And  yet  the  series  that  partially 
bridges  the  gap  is  great  enough  and  significant  enough 
to  require  pointed  recognition  and  sharp  emphasis  as  one 
of  the  most  suggestive  factors  in  the  earth's  evolution. 
The  reason  for  the  present  imperfection  of  this 
theoretical  series  lies,  perhaps,  in  the  destructive 
efficiency  of  the  lower  orders-  of  life.  Ever  since  the 
minute  forms  of  life  filled  the  earth  with  their  multitude, 
the  slow  graded  steps  by  which  alone  the  long  chain  of 
syntheses  could  be  accomplished  have  been  subject  to 
formidable  predacious  attacks.  The  ubiquity,  the 
voraciousness,  and  the  digestive  efficiency  of  the  multi- 
tude of  minute  pioneers  in  the  living  kingdom  may  well 
be  supposed  not  only  to  have  destroyed  the  relics  of  the 
primitive  series  but  to  have  broken  down  all  subsequent 
attempts  before  the  long  ascensive  chain  could  be  com- 
pleted. The  universality,  the  persistency,  and  the 
effectiveness  of  the  attacks  of  bacteria  and  their  kin 
upon  highly  complex  carbon  compounds,  while  yet  in 
their  formative  states,  seem  adequate  to  inhibit  entirely 
a  process  that  might  have  been  successful  before  their 
advent.  There  is  fossil  evidence  of  the  presence  and  of 
the  destructive  work  of  bacteria  far  back  in  the  geologic 
ages.  There  is  inferential  evidence  of  their  presence  and 
destructive  work  as  far  back  as  the  stratigraphic  record 
of«  life  reaches. 

APPEARANCE   OF   LIVING   ORGANISMS 

Nothing  in  the  whole  genetic  history  of  the  earth  was 
more   distinctive   than   the   first   appearance   of  living 


ORGANIZATION  IN  GREAT  CONTACT  HORIZONS     245 

organisms.  Nothing  is  more  remarkable  than  the 
persistency  with  which  these  organisms  have  since  occu- 
pied the  surface  of  the  land,  the  bottom  of  the  air,  the 
surface  of  the  waters,  and  the  bottoms  of  the  waters. 
They  wander  indeed  somewhat  from  the  immediate 
contact  surfaces,  but  none  the  less  they  adhere  rather 
faithfully  to  them  or  to  their  vicinity.  If  scrutinized 
more  closely,  it  is  seen  that  the  critical  conditions  for  the 
living  world  are  best  satisfied  when  the  three  factors, 
earth,  air,  and  water,  unite  their  good  offices  with  those 
of  radiant  energy,  which  appears  to  be  quite  as  vital  a 
factor  in  the  combination  as  either  of  the  material 
factors.  We  are  perhaps  inclined  to  regard  radiant 
energy  as  even  more  indispensable  than  the  others,  but 
nothing  is  more  inhibitive  of  life  than  certain  intensities 
of  radiant  energy.  It  is  a  remarkable  combination, 
conditioned  by  singularly  narrow  limitations. 

From  our  personal  and  racial  point  of  view,  the 
transcendent  nature  of  the  initiation  of  life  needs  no 
insistence.  Our  personal  and  racial  point  of  view  may 
not  be  without  its  element  of  partiality,  but,  con- 
sidered strictly  as  a  problein  of  research,  the  intro- 
duction of  processes  so  different  from  those  of  the 
cosmogonic  ages  as  are  cell  construction,  co-operative 
physiological  action,  adaptation  to  ends,  the  propagation 
of  kind,  and  the  perpetuation  of  species,  constitutes 
perhaps  the  most  puzzling  aspect  of  terrestrial  genesis, 
unless  it  be  the  one  that  is  to  follow.  There  is,  in  these 
processes,  a  subtle  factor  not  distinctly  betrayed  in  the 
earlier  modes  of  evolution,  though  it  may  have  been 
there.  It  is  hard  to  find  any  distinct  trace  of  an  organ- 
izing, correlating,  directive  factor,  as  such,  in  even  the 


246  THE  ORIGIN  OF  THE  EARTH 

most  intricate  of  the  inorganic  syntheses,  and  yet  there 
are  subtle  intimations  of  something  of  the  kind  in  the 
complexity  of  even  inorganic  combinations. 

It  is  not  clear  from  any  positive  knowledge  at  present 
available  that  there  was  present  in  the  initial  stages  of 
life-evolution  any  sentient  or  psychological  element, 
and  yet  cell  construction,  with  its  apparent  adaptation 
to  ends  not  necessarily  confined  to  its  own  immediate 
economy,  co-operative  physiological  action,  with  its 
relations  to  the  life  of  members  not  immediately  involved 
in  the  action,  provision  for  the  propagation  of  kind,  with 
transmitted  powers  of  reproduction,  and  precautions 
for  the  perpetuation  of  the  species,  squint  sharply  in  the 
direction  of  psychological  endowments. 

ADVENT   OF    THE   PSYCHOLOGICAL 

However  occultly  the  psychological  element  may  have 
crept  into  the  advancing  life-series,  its  distinct  appear- 
ance marked  the  climax  of  the  earth's  evolution.  It  is 
the  last  factor  in  the  earth's  genesis,  and  the  most 
enigmatical.  Considered  with  respect  to  its  own 
inherent  qualities,  the  psychological  factor  seems  to 
stand  apart  from  the  physiological  farther  even  than  does 
the  physiological  from  the  inorganic.  The  bridging  of 
the  gap  is  less  explicable,  scientifically  and  philo- 
sophically. The  distinctive  qualities  of  the  psycho- 
logical world  are  not  commonly  recognized  in  scientific 
interpretations  of  the  physiological  or  of  the  inorganic 
worlds;  but  the  gradation  from  the  seemingly  insentient 
and  merely  physiological,  as  embodied  in  the  lowest 
orders  of  living  beings,  to  the  earliest  types  of  sen- 
tient life,  and  thence  on  to  the  highest  manifestations  in 


ORGANIZATION  IN  GREAT  CONTACT  HORIZONS      247 

the  thinking  world,  is  so  intimate  as  to  bind  the  whole 
into  one  inextricable  problem.  If  the  qualities  of  the 
psychological  world  were  potential  in  the  factors  that 
entered  into  the  earlier  stages  of  the  earth's  genesis, 
a  revision  of  our  conception  of  those  factors  is  logically 
required.  Fundamentally,  the  antecedents  can  scarcely 
be  less  comprehensive  than  the  consequents.  If  the 
material  begets  the  spiritual,  the  material  can  hardly  be 
altogether  material.  If  the  mechanistic  indulges  in 
research,  it  cannot  well  be  altogether  mechanistic. 

Our  province,  however,  lies  rather  with  the  geologic 
conditions  that  attended  the  origin  of  terrestrial  life 
and  of  psychic  action,  than  with  their  ultimate  nature 
and  their  fundamental  relations. 

EARLY   BIOGENETIC   CONDITIONS 

Under  the  planetesimal  hypothesis,  the  progressive 
work  of  uniting  solar  and  other  energies  with  carbon, 
hydrogen,  oxygen,  nitrogen,  sulphur,  phosphorus,  potash, 
and  other  elements,  into  a  synthetic  chain  which  led  up 
to  biotic  and  psychic  organisms,  found  suitable  conditions 
at  an  early  stage  of  the  earth's  juvenile  history.  As 
already  observed,  the  ascending  synthetic  series  was 
free  from  the  adverse  effects  of  its  own  development, 
free  from  predaceous  attacks  by  minute  organisms,  now 
a  formidable  obstacle  to  such  an  evolution.  Syn- 
thetic combinations  were  free  to  go  to  the  utmost 
lengths  to  which  inherent  organizing  forces  impelled, 
except  as  restrained  by  inorganic  limitations.  The 
essential  conditions  of  heat,  light,  air,  water,  and 
earth  surface  are  not  pictured  as  then  radically 
different  from  those  of  the  later  geologic  ages  and 


248  THE  ORIGIN  OF  THE  EARTH 

of  the  present,  though  not  altogether  identical  with 
them. 

The  sun  was  indeed  younger  in  those  ages  and,  under 
current  views  of  stellar  evolution,  more  intensely  radiant, 
but  the  nebulous  material  that  intervened  between  the 
sun  and  the  young  earth  should  have  cut  off  some 
part  of  the  solar  radiance.  However,  there  should  have 
been  compensation  in  the  heat  and  light  generated  by 
the  plunge  of  planetesimals  into  the  upper  atmosphere. 
The  ratio  of  such  compensation  is  uncertain;  it  is 
merely  evident  that  the  planetesimal  interferences  and 
the  planetesimal  compensations  followed  the  same  law, 
and  that,  as  both  died  gradually  away,  the  penetration 
of  the  radiance  of  the  sun  grew  toward  its  full  unob- 
structed power.  If  the  joint  effects  of  these  in  the 
earliest  ages  of  growth  were  prohibitory,  they  gradually 
gave  place  to  those  that  were  permissory. 

The  inherent  influences  of  the  atmosphere  of  the 
early  .stages  of  growth  were  doubtless  more  comparable 
to  those  of  Tibetan  and  Titicacan  regions  today  than  to 
those  of  tropical  lowlands.  The  atmosphere  was  rela- 
tively thin,  its  pressure  low,  its  content  of  moisture 
limited.  The  normal  effects  of  these  properties  should, 
apparently,  have  tended  toward  aridity  and  low  tempera- 
ture. The  atmosphere  itself,  however,  should  have  been 
ultra-Krakatoan  in  its  burden  of  planetesimal  dust,  and 
the  young  earth  was  thus  blanketed  against  intensities 
of  radiance  from  without  and  inequalities  of  radiation 
from  within.  But  no  amelioration  of  variations  could 
probably  offset  the  forces  of  atmospheric  circulation; 
the  descending  currents  were  almost  inevitably  dry, 
and  the  ascending  currents  precipitant,  after  sufficient 


ORGANIZATION  IN  GREAT  CONTACT  HORIZONS     249 

moisture  had  been  acquired;  before  that,  the  initiation 
of  life  was  inhibited.  We  assume,  therefore,  that  life- 
genesis  was  conditioned  by  greater  or  lesser  variations  of 
moisture  and  dryness,  and  hence  of  freshness  and  salinity 
of  waters,  and  that  these  were  added  to  the  variations  of 
radiant  energy.  Mild  variations  were  doubtless  helpful, 
violent  variations  destructive. 

The  surface  conditions  in  the  growing  stages  should 
have  been  rather  those  of  eolian  deposition  and  wind 
driftage  than  those  of  aqueous  deposition  and  stream 
erosion,  but  the  two  processes  must  have  joined  their 
effects  so  soon  as  water  action  became  an  effective 
agency.  The  billowy  configuration  of  a  dune  surface 
was  probably  more  characteristic  throughout  the  stages 
of  active  growth  than  the  gullies  and  trenches  of  a  highly 
humid  region;  probably  the  former  chiefly  preponder- 
ated in  the  areas  of  descending  air,  while  the  latter  took 
precedence  in  the  tracts  of  ascending  air  and  gained  in 
general  dominance  as  time  went  on.  Dunes  formed  of 
plane tesimal  dust  should,  however,  have  been  far  less 
inhospitable  to  the  dawning  life  than  modern  dunes  of 
coarse,  well-rolled,  siliceous  sand. 

The  growing,  billowy,  porous  surface  of  the  juvenile 
earth  very  definitely  conditioned  the  early  stages  of  the 
increasing  hydrosphere.  The  first  surplus  of  waters 
condensed  from  the  growing  atmosphere  would  obviously 
have  been  absorbed  in  the  deep  porous  mantle  of  plane- 
tesimal  dust  and  planetesimal  residuals  that  had  been 
gathered  to  the  earth;  only  later,  and  very  gradually, 
would  the  increasing  waters  emerge  at  the  bottoms  of 
the  basins;  only  much  later  would  great  water-bodies 
appear.  If  our  picture  of  the  surface  configurations  is 


250  THE  ORIGIN  OF  THE  EARTH 

true,  the  basins  in  the  billowy  eolian  surface  were  almost 
without  number,  and  the  first  surface  aspect  of  the 
hydrosphere  was  that  of  a  countless  multitude  of  pools 
and  lakelets.  From  these,  in  time,  grew  lakes  and  seas, 
and  at  length  the  oceans. 

The  organizing  processes  that  led  up  to  the  biologic 
and  psychic  kingdoms  may  quite  probably  have  entered 
upon  their  long  career  as  soon  as  the  hydrosphere  began 
to  emerge  at  the  surface,  for,  with  the  low  pressure 
of  the  early  atmosphere,  the  temperature  of  the  water 
could  scarcely  have  been  prohibitory.  While  we  may 
not  fix,  with  any  confidence,  the  time  when  the  hydro- 
sphere would  reach  this  stage,  we  may  make  this  stage 
a  fair  index  of  the  time  when  general  physical  conditions 
were  probably  hospitable*  to  life.  Starting  at  this  stage 
the  organizing  process  may  have  run  parallel  with  the 
remaining  large  part  of  the  earth's  growth.  In  view  of 
this,  the  advanced  state  of  deployment  and  differentia- 
tion which  life  presented  at  the  time  its  first  good  record 
was  made  in  the  Cambrian  Period  is  shorn  of  the  sur- 
prising features  it  bore  when  regarded  from  the  older 
point  of  view,  for  under  that  view  the  initiation  of  life 
was  necessarily  delayed  until  after  the  whole  gaseous 
spheroid  had  condensed  into  the  molten  globe  and  the 
molten  globe  had  cooled  to  a  suitable  temperature.1 

INITIAL   BIOLOGIC   HABITAT 

It  has  been  the  habit  of  geologists  and  biologists 
alike  to  think  of  the  ocean  as  the  probable  habitat  of  the 
earliest  forms  of  life,  and  not  unnaturally  so;  the  larger 
part  of  the  imperfect  record  of  early  life  was  preserved 
in  marine  deposits.2  It  was  further  noted  that  there 


ORGANIZATION  IN  GREAT  CONTACT  HORIZONS     251 

were  evolutions  of  marine  forms  into  terrestrial  forms; 
there  were,  to  be  sure,  evolutions  of  land  forms  into 
marine  forms,  but  these  were  easily  interpreted  as  later 
reactions.  An  oceanic  genesis  of  life  was  favored  by  the 
inherited  theory  of  the  preponderance,  if  not  the  uni- 
versality, of  the  primitive  ocean.  The  dominance  of  the 
primitive  ocean  was,  however,  essentially  a  cosmogonic 
deduction.  The  assumption  of  even  the  existence  of  a 
vast  oceanic  envelope,  at  the  time  life  appeared  on  the 
earth,  has,  indeed,  little  other  basis  than  is  derived 
from  some  theory  of  the  earth's  origin.  The  oceanic 
view  of  the  origin  of  life  is  therefore,  at  bottom,  little 
more  than  a  cosmogonic  assumption.  It  is,  to  be  sure, 
largely  a  subconscious  cosmogonic  assumption,  but  the 
fact  that  it  is  so  largely  subconscious  does  not  add  a 
whit  to  its  cogency.  The  assumption  that  anything 
which  can  properly  be  called  an  ocean  existed  at  the 
time  life  was  initiated  is  necessarily  challenged  in  any 
critical  inquiry  that  scrutinizes  the  ground  of  each  postu- 
late, conscious  or  subconscious.  The  initiation  of  life 
required,  indeed,  at  least  the  beginnings  of  a  hydro- 
sphere, but  the  presence  of  an  ocean  needs  either  logical 
or  evidential  support.  It  may,  of  course,  be  that  the 
first  favorable  conditions  for  life  were  not  attended  by 
the  generation  of  the  first  forms  of  life,  and  that  the 
initiation  of  life  was  delayed  until  an  ocean  was  evolved, 
but  if  the  generation  of  life  was  a  naturalistic  process,  it 
is  theoretically  obligatory  on  the  advocate  of  delay  to 
show  why  the  process  should  not  have  proceeded  when 
the  essential  conditions  were  fulfilled.  Chemi co-physical 
reactions  usually  take  place  when  the  elements  are 
brought  together  under  suitable  conditions.  The  record 


252  THE  ORIGIN  OF  THE  EARTH 

also  has  its  suggestions.  The  time  required  for  so  great 
evolutionary  work  as  is  implied  by  the  wide  deployment 
of  life  in  Cambrian  times  is  such  as  to  tax  even  the  high- 
est probabilities  of  the  available  lapse  of  time.  The  exi- 
gencies of  time  render  the  introduction  of  life  as  early 
as  the  requisite  conditions  permitted,  extremely  prob- 
able. There  appear  to  be  no  inherent  grounds  for 
hypothetically  delaying  the  initiation  of  life  till  the 
oceans  grew  to  be  vast  and  saline.3 

In  the  growth  of  the  juvenile  earth,  as  already  noted, 
the  first  waters  should  have  condensed  from  water-vapor 
held  in  the  primitive  atmosphere,  the  infantile  hydro- 
sphere growing  very  gradually  from  the  infantile 
atmosphere.  Obviously  the  first  waters  would  have 
been  absorbed  into  the  deep  porous  layer  enveloping  the 
earth-body  and  would  have  crept  up  only  gradually  to  the 
bottoms  of  the  hollows  that  accidented  the  surface, 
and  so,  as  already  noted,  the  first  appearance  of  the 
hydrosphere  at  the  surface  should  have  taken  the  form 
of  innumerable  pools  or  lakelets,  more  or  less  pro- 
miscuously scattered  over  the  surface  of  the  juvenile 
earth.  The  question  of  the  probable  bio-genetic 
habitat,  under  the  planetesimal  view,  seems  thus  nar- 
rowed to  an  alternative  between  the  pools  and  the  well- 
watered  lands,  or  else  the  shorelines  between  these. 

What  appear  to  have  been  the  special  demands  of  the 
case? 

i.  An  adequate  supply  of  radiant  energy  and  an  ade- 
quate protection  against  the  destructive  effects  of  radiant 
energy. — These  could  probably  be  furnished  by  selected 
depths  in  either  the  surface  soils  of  the  lands  or  in*  the 
open  waters  of  the  pools  and  lakelets. 


ORGANIZATION  IN  GREAT  CONTACT  HORIZONS    253 

2.  An  adequate  supply  of  carbon,  oxygen,  nitrogen, 
carbon  dioxide,  water,  and  combinations  of  these,  together 
with  lesser  quantities  of  phosphorous,  sulphur,  potash,  and 
other  alkalies  and  alkaline  earths,   and  various  earthy 
substances. — All  these  could  best  be  supplied  by  the 
soil  waters,  but  could  doubtless  be  found  in  the  waters 
of  the  pools  and  the  lakelets.     The  soils  were  of  course 
then  purely  inorganic. 

3.  An  adequate  mechanism  for  holding,  protecting,  and 
preserving  the  products  of  each  synthetic  step  in  such  a  way 
as  to  favor  the  next  synthetic  step. — A  continuous  series 
of   such   well-conserved   inheritances   seems   a   critical 
prerequisite  to  the  long  succession  of  steps  involved  in 
the  complete  evolution.     The  pores  of  the  soil  seem 
better  suited  to  this  than  the  free  waters.     The  effects 
of  open  agitated  water  should  have  been  diffusive  and 
dispersive.     The  pores  of  the  soil  probably  only  fur- 
nished a  first  aid;    a  more  specific  mode  of  inclosure, 
protection,  and  promotion  perhaps  grew  out  of  this,  as 
noted  below. 

4.  A  circulatory  mechanism  to  bring  suitable  supplies 
for  the  new  combinations,  to  concentrate  these  supplies 
in  proper  measure,  and  to  carry  away  the  unused  and 
perhaps  deleterious  portion. — These  are  functions  which 
must  be  subserved  in  some  way  by  the  mechanism  of 
every  living  organism.     After  such  organisms  had  once 
come  into  being,  they,  of  themselves,  developed  ana- 
tomical  devices   that  fulfilled   these   essential  require- 
ments, but  in  the  long  generative  process  preceding  the 
acquisition  of  such  powers,  some  crude  substitute  for 
such  a  mechanism,  incidentally  furnished  by  the  inor- 
ganic environment,  was  probably  prerequisite  to  the 


254  THE  ORIGIN  OF  THE  EARTH 

completion  of  the  ascensive  chain.  Such  a  mechanism, 
crudely  serviceable  for  the  time,  was  perhaps  found 
in  the  normal  circulation  that  prevails  within  soils  suit- 
ably situated. 

A  multitude  of  special  situations  were  presented,  but 
perhaps  those  that  best  fulfilled  the  requirements  were 
found  in  the  soils  of  the  shore  tracts  that  girt  the  pools 
and  lakelets,  or  in  the  soils  of  the  forelands  that  lay 
between  these  and  the  uplands.4  (We  use  the  term  soil  of 
course  in  its  inorganic  sense.)  In  these  foreland  and 
shoreland  soils  there  should  have  been  an  ample  supply 
of  water  while,  at  the  same  time,  the  fluctuations  of  the 
water-level  should  have  been  limited  wherever  the  con- 
trolling water-level  of  the  adjacent  pools  or  lakelets 
was  regulated  by  adequate  outlets.  The  drainage 
from  the  uplands,  passing  slowly  beneath  the  forelands 
and  shorelands,  should  have  given  an  adequate  and 
perennial  supply  of  all  the  solutions  requisite  for  the 
successive  synthetic  combinations;  while  the  sloping 
surfaces  should  have  given  adequate  super-drainage 
and  the  requisite  aeration.  Capillary  action  should 
have  drawn  graduated  supplies  of  water,  carrying  solu- 
tions, emulsions,  and  suspensions  of  various  con- 
centrations, up  to  heights  in  the  soil  which  varied  with 
conditions,  while  the  larger  pores  and  the  upper  levels 
were  filled  with  air  communicating  with  the  open 
atmosphere.  In  a  word,  there  was  a  reticulation  of 
capillary  water  reaching  up  with  diminishing  branches, 
from  the  water-level  below,  and  a  reticulation  of  air 
reaching  down,  with  attenuating  branches,  from  the 
atmosphere  above,  the  two  interlocking  in  a  most 
intricate  way.  Each  of  these  advanced  and  retreated, 


ORGANIZATION  IN  GREAT  CONTACT  HORIZONS     255 

reciprocally,  as  times  of  wetness  and  times  of  dryness 
came  and  went,  but  the  mutual  action  of  the  two  main- 
tained a  graded  intermingling  6f  air  and  water  that,  in 
later  ages,  has  been  of  the  utmost  importance  to  soil- 
life,  and  was  perhaps  of  equal  importance  to  its  initiation. 
There  should  have  been  intermittent  water  supplies 
from  the  clouds,  and  constant  supplies  by  capillary 
action  from  below,  while  soil  breathing,  actuated  by  the 
pulsations  of  the  atmosphere,  should  have  been  an 
effective  agency  in  promoting  a  steady  and  controlled 
evaporation  from  the  surfaces  of  the  interlocking  net- 
work of  water.  Evaporation  above  and  capillary  supply 
below,  varied  by  precipitation,  should  have  promoted 
a  gentle,  but  effectual  and  perpetual,  circulation  con- 
ducive both  to  concentrations  and  to  re-solutions,  in 
turn,  as  wetness  and  dryness  alternated.  The  analogy 
of  such  a  soil  circulation  to  the  circulatory  system  of 
plants  is  very  close,  and  the  one  may  well  have  been 
ancestor  to  the  other.  Such  a  circulatory  system  was 
inevitable  in  the  early  soils  under  the  general  conditions 
postulated. 

Obviously  open  waters,  while  not  without  their  system 
of  surface  exchange  with  the  atmosphere,  present  no  inter- 
stitial circulatory  system  which  rivals  that  of  the  soils. 

5.  A  supplementary  mechanism  by  which  osmotic  action 
would  be  called  into  play  with  increase  of  efficiency  in  the 
concentration  and  combination  of  the  requisite  constituents, 
while  at  the  same  time  cell-like  inclosure  of  the  synthetic 
compounds  progressively  formed  would  keep  them  in  close 
working  relations. 

While  almost  all  substances  are  susceptible  of  taking 
on  the  colloidal  state,  it  is  actually  assumed  about  in 


256  THE  ORIGIN  OF  THE  EARTH 

proportion  to  the  complexity  of  the  chemical  composi- 
tion. In  compliance  with  this  general  rule,  the  chain 
of  ascending  carbon  compounds  that  led  up  to  the  organic 
type  seem  to  have  been  attended  by  a  parallel  increase 
in  the  proportion  of  colloids  to  crystalloids.  At  any 
rate,  the  colloids  are  highly  preponderant  in  the  tissues 
of  living  beings.  The  fluent  forms,  the  pliancy,  and  the 
easy  assumption  of  membranous  shapes,  so  characteristic 
of  colloids,  as  notably  fitted  these  to  take  on  structures 
of  the  organic  type,  as  the  angular,  rigid  forms  of  crystal- 
loids unfitted  them  for  like  use.  The  suggestion  at 
once  follows  that  the  progressive  development  and  con- 
centration of  colloids  may  have  been  as  indispensable 
to  progress  toward  the  formation  of  organic  structures, 
as  was  complex  chemical  combination.  The  singular 
distributions  and  adjustments  of  energy  in  the  colloid 
state,  so  far  as  developed  in  the  lower  carbon  com- 
pounds, may  have  been  an  essential  aid  to  the  next 
higher  steps  in  chemical  complexity.  This  at  least  may 
serve  as  a  suggestion  of  a  possible  line  of  evolution. 

Even  in  the  inorganic  world,  certain  of  the  carbon 
compounds  are  prone  to  assume  the  colloid  state.  Ade- 
quate supplies  of  hydrocarbons  and  other  simple  carbon 
compounds  that  habitually  take  on  the  colloidal  state 
could  scarcely  have  been  wanting  in  the  juvenile  earth. 
In  addition  to  general  sources,  there  was  perhaps  a 
special  source  of  peculiar  adaptability  to  the  process 
now  under  study.  The  carbon  of  the  sun  in  passing  from 
its  intensely  heated  state  into  the  nebulous  condition 
would  not  improbably  take,  in  part  at  least,  the  form  of 
carbides  analogous  to  those  found  in  meteorites.  These, 
in  coming  into  contact  with  air  and  moisture,  would 


ORGANIZATION  IN  GREAT  CONTACT  HORIZONS    257 

become  reactive  and  form  carbon  compounds  of  higher 
complexity,  some  of  which  are  prone  to  take  on  the 
colloidal  state.  It  is  not  improbable,  therefore,  that  the 
accessions  of  planetesimals  brought  carbides,  as  well 
as  nitrides,  chlorides,  silicides,  sulphides,  and  phosphides, 
into  the  growing  earth-mantle,  and  that  the  spontaneous 
reactions  of  these  supplied  the  ground-waters  with 
carbon  compounds  of  growing  complexity  and  increased 
colloidality.  These,  as  fast  as  formed,  would  be  floated 
to  the  water  surface  and  so  enter  the  capillary  circula- 
tion of  the  soils  and  be  susceptible  of  such  further 
combinations  as  might  await  them  there. 

The  interlocking  reticulum  of  capillary  waters  and 
air  ducts  in  the  soils  needs  now  to  be  pictured  a  little 
more  closely.  In  the  layers  of  most  effective  inter- 
mingling of  air  and  water,  water  films  surround  each 
soil  grain.  These  grow  thicker  or  thinner,  or  dry  up 
entirely,  as  changes  from  humidity  to  aridity,  or  the 
reverse,  take  place.  The  sharper  angles  between  grains, 
the  smaller  pores,  and  the  narrower  passages  between  the 
larger  inter-grain  spaces  are  normally  filled  with  capillary 
waters  likewise  subject  to  come  and  go  with  increasing 
wetness  and  dry  ness.  The  larger  pores  and  passage- 
ways, and  inter-grain  spaces,  are  normally  filled  with  air. 
These  also  advance  or  withdraw,  grow  or  shrink,  as  the 
state  of  wetness  and  dry  ness  varies.  The  whole  forms 
an  intricate  plexus  of  water  films  and  capillary  concentra- 
tions of  water,  interpenetrated  with  air  ducts.  This 
picture,  drawn  from  modern  soils,  may  be  transferred, 
with  some  increase  of  sharpness,  to  the  soils  of  the 
growing  earth,  free  from  rootlets  and  minute  organisms, 
as  well  as  their  relics,  and  their  interferences.  Our 


258  THE  ORIGIN  OF  THE  EARTH 

interest  centers  on  the  progressive  concentrations  and 
deposits  that  would  take  place  in  the  passageways  and 
intergranular  cavities  in  the  upper  soils  as  the  result  of 
continued  capillary  supply  and  continued  evaporation 
in  situations  where  leaching  was  unable  to  remove  these 
concentrates  and  deposits,  as  must  have  been  the  case 
in  a  multitude  of  places  in  regions  prone  to  aridity.  As 
the  soil  waters  were  progressively  evaporated,  the 
solutions,  emulsions,  and  suspensions  borne  by  them 
were  concentrated  and,  in  part,  deposited  as  solid  films, 
threads,  or  lumps  in  which  colloids  and  crystalloids 
must  have  mingled,  much  as  they  were  mingled  in  the 
waters.  As  wet  and  dry  seasons  came  and  went,  there 
must  have  been  alternations  of  deposit  and  partial  re- 
solutions, with  the  general  result  that,  in  some  situa- 
tions at  least,  the  plexus  of  films  grew  thicker  and  more 
membrane-like,  the  pores  and  passageways  were  more 
and  more  closed,  concentrated  solutions  and  emulsions 
were  more  and  more  liable  to  be  entrapped  and  isolated 
in  the  inter-grain  spaces,  and,  when  so  entrapped,  to 
be  completely  inclosed  iSy  films  formed  over  their  own 
exposed  surfaces,  thus  tending  more  and  more  to  con- 
vert the  open  reticulum  into  a  cellular  reticulum.  In 
many  a  case,  no  doubt,  the  process  went  on  until  the 
whole  mass  of  soil  was  cemented  into  a  continuous  solid 
by  the  asphaltic  residue  of  the  hydrocarbons,  and  the 
precipitated  salts,  or  by  mixtures  of  these;  but  before 
these  ultra-results  were  reached,  there  would  probably 
be  much  closure  of  constricted  passages  between  larger 
spaces  -by  films  formed  from  the  concentrates  and  so  a 
cellular  structure  should  not  only  generally  precede 
complete  cementation,  but  should  develop  widely 


ORGANIZATION  IN  GREAT  CONTACT  HORIZONS    259 

where  the  latter  extreme  was  never  reached.  In  the 
course  of  this  progressive  growth  of  enwrapping  films 
and  closure  of  connecting  passages,  soil  waters,  ap- 
proaching saturation,  entrapped  in  cavities  by  films 
formed  over  their  exposed  surfaces,  constituted  the 
cell-filling  and  were  subject  to  further  concentra- 
tion and  combination.  It  seems  inevitable  that 
within  the  soils  of  the  land  surface  subject  to  such 
conditions  there  should  have  grown  up,  thus  inorgani- 
cally and  inevitably,  not  only  thousands  and  millions, 
but  billions  and  trillions  of  crude  capsules  which 
thus  came  to  serve  a  new  function  in  the  synthetic 
process. 

Obviously  the  colloids  were  best  fitted  by  nature  to 
form  films  and  membranes.  Probably  the  crystalloids 
were,  on  the  whole,  more  subject  to  re-solution  and 
removal,  giving  various  degrees  of  porosity  to  the 
residual  membranes.  Various  degrees  of  imperviousness 
and  porosity  may  therefore  be  assigned  to  the  crude 
membranes  so  formed. 

Now,  as  soon  as  concentrates  of  colloids  and  crystal- 
loids were  thus  inclosed,  cell-fashion,  in  more  or  less 
porous  membranes,  the  mechanism  for  osmotic  action 
was  provided.  When  the  wet  season  returned,  osmotic 
action  should  ensue.  The  colloids  within  the  inclosure 
should  be  retained  by  the  inclosing  membranous  walls, 
while  crystalloids,  so  far  as  they  passed  into  solution, 
might  traverse  these  walls  in  either  direction,  as  the 
state  of  concentration  might  require.  Thus  a  new 
agency,  peculiarly  fitted  for  colloidal  concentration,  as 
well  as  a  special  means  of  colloidal  retention,  should 
have  been  brought  into  action.  Conjointly,  these 


260  THE  ORIGIN  OF  THE  EARTH 

qualities  might  apparently  contribute  very  essentially 
to  the  further  progress  of  synthesis. 

The  new  agencies  thus  instituted  would  bear  a  very 
close  analogy  to  the  function  of  cell-inclosure  and  osmosis 
that  forms  the  working  mechanism  of  plants. 

With  the  development  of  this  quasi-cellular  structure 
and  this  initiation  of  osmotic  action  between  a  colloid 
content  within  and  the  soil-solutions  without,  the  limits 
to  which  the  premises  of  the  geologist  warrant  him  in 
going  seem  to  have  been  reached.  The  further  solution 
of  the  problem  of  synthetic  ascent  seems  to  fall  into  the 
fields  of  the  organic  chemist,  of  the  colloid  chemico- 
physicist,  of  the  biologist,  and  of  the  psychologist. 

It  need  only  be  further  remarked  here  that  erosions, 
transportations,  and  redepositions,  actuated  by  wind 
and  water,  working  on  surfaces  devoid  of  vegetal  pro- 
tection, should,  at  frequent  intervals,  have  displaced, 
dispersed,  and  replanted  a  part  of  the  quasi-cellular 
aggregates,  and  thus  have  seeded,  as  it  were,  a  multitude 
of  new  situations  with  new  possibilities,  favorable  and 
unfavorable  for  further  progress.  The  pools  and  the 
lakelets  should  have  been  thus  implanted,  so  that  if  they 
offered  conditions  favorable  for  the  further  progress 
of  the  synthetic  process,  the  advantage  would  have 
been  embraced. 

A  distinguishing  characteristic  of  the  organic  mechan- 
ism is  its  singular  adaptation  to  mild  temperatures  and 
gentle  reactions,  and  its  singular  efficiency  under  these 
conditions.  The  living  body,  whether  plant  or  animal,  is 
a  mild-temperature  engine.  It  eschews  intensities  and 
wide  fluctuations.  Its  best  work  is  done  under  equable 
conditions  or  mild  oscillations.  This  gives  strength  to 


ORGANIZATION  IN  GREAT  CONTACT  HORIZONS    261 

the  presumption  that  life  came  into  function  under  con- 
ditions as  similar  as  might  be  to  those  equable  and 
gentle  oscillatory  states  of  earth,  air,  water,  and  insola- 
tion, that  have  ever  since  contributed  to  its  best  activ- 
ities. Perhaps  there  is  no  fact  in  the  earth's  career 
more  remarkable  than  the  fidelity  with  which  the  very 
narrow  ranges  of  temperature,  and  the  not  less  narrow 
ranges  of  atmospheric  constituents  essential  to  the  evo- 
lution of  life,  have  been  maintained,  while  oscillations 
within  these  permissible  ranges  have  freely  prevailed. 
These  limits  and  these  oscillations  were  perhaps  as 
imperative  for  life's  origin  as  for  its  prolonged  main- 
tenance. 

Perhaps  the  supreme  criterion  to  which  a  hypothesis 
of  the  genesis  of  the  earth,  of  the  mode  of  its  growth,  and 
of  the  evolution  of  its  inhabitants  can  be  submitted— 
next  after  its  complete  fulfilment  of  the  specific  require- 
ment of  the  historic  vestiges  embodied  in  itself  and  in 
its  ongoings — is  the  fitness  and  the  adequacy  of  its 
postulates  for  the  task  of  maintaining,  throughout  all 
the  earth's  adolescent  and  adult  stages,  those  delicate 
conditions  that  have  made  possible  the  long  sequence 
of  life  and  its  wonderful  ascent.  The  fidelity  with  which 
life  has  been  furnished  a  suitable  environment  for  the 
uninterrupted  pursuit  of  its  ascensive  career,  and  the 
unbroken  continuity  with  which  the  requisite  sources 
of  supply  have  been  maintained,  may  well  be  regarded  as 
the  profoundest  expression  of  the  law  of  equilibrium 
manifested  in  the  long  course  of  the  earth's  history. 

It  is  our  personal  view  that  what  we  conveniently 
regard  as  merely  material  is  at  the  same  time  spiritual, 


262  THE  ORIGIN  OF  THE  EARTH 

that  what  we  try  to  reduce  to  the  mechanistic  is  at  the 
same  time  volitional,  but  whether  this  be  so  or  not, 
the  emergence  of  what  we  call  the  living  from  the  inor- 
ganic, and  the  emergence  of  what  we  call  the  psychic 
from  the  physiologic,  were  at  once  the  transcendent  and 
the  transcendental  features  of  the  earth's  evolution. 

REFERENCES 

1.  Chamberlin    and    Salisbury,    "The    Abrupt   Appearance  of   the 
Cambrian  Fauna,"  Geology,  II,  111-15. 

2.  W.  K.  Brooks, "The Origin  of  the  Oldest  Fossils  and  the  Discovery 
of  the  Bottom  of  the  Ocean,"  Journal  of  Geology,  II  (1804),  455-79- 

3.  T.  C.  Chamberlin,  "On  the  Habitat  of  the  Early  Vertebrates," 
Journal  of  Geology,  VIII  (1900). 

4.  T.  C.  Chamberlin  and   R.  T.  Chamberlin,  "Early  Terrestrial 
Conditions  That  May  Have  Favored  Organic  Synthesis,"  Science,  N.S., 
XXVII,  No.  730,  (December  25,  1908),  897-911. 


INDEX 


Acknowledgements,  x. 

Adams,  F.  D.,  177,  224. 

Adaptation  to  tidal  action,  190. 

Aggregation:  from  circular  con- 
centric orbits,  60;  from  hetero- 
geneous elliptical  orbits,  60; 
of  nebulous  matter,  145. 

Alaska-Siberian  bridge,  211,  220. 

Alloys,  metallic,  240. 

Alps-Himalaya  tract,  213. 

Alternates,  law  of,  221. 

Angulations,  207,  208. 

Antillean  view  of  globe,  207. 

Antipodal  features,  219,  220. 

Antipodal  positions,  218. 

Apophyses,  193,  203. 

Appearance  of  living  organism,  244. 

Aridity,  8. 

Ascending  currents,  248. 

Atmosphere:  circulation  of,  195; 
collisional,  22;  co-operation  of, 
with  lithosphere  and  hydro- 
sphere, 168;  depletion  of,  7; 
escape  of,  31;  krenal,  20,  21,  22, 
157  (of  the  sun),  26;  modify- 
ing influences  of,  193;  of  the 
sun,  26;  orbital,  21,  22,  157  (of 
the  sun),  26;  primitive,  166; 
sources  of,  165;  supplementary 
agencies  acting  on,  27;  ultra, 
21,  22,  27,  59,  144  (of  the  sun), 
26;  white-hot  stage,  34. 

Atmospheres,  157;  interchange  of, 
32;  planetary,  26,31. 

Atmospheric  interchanges  and 
equilibria,  25. 

Atmospheric  maintenance,  32. 

Atmospheric  reciprocity,  27. 


Babinet,  50. 

Backbone  of  Brazil,  207,  208. 

Bacteria,  attacks  of,  244. 

Basal  features  of  greater  configu- 
rations, 200. 

Basal  framework,  213. 

Basaltic  columns,  186,  187. 

Basins,  oceanic,  217. 

Becke,  F.,  225. 

Becker,  G.  F.,  225. 

Billowy  configuration  of  primitive 
dune  surface,  249. 

Biogenetic  conditions,  early,  247. 

Bio-genetic  habitat,  252;  initial, 
250. 

Biologist,  260. 

Bi-parental  origin,  101. 

Bode's  formula,  152. 

Bridge,  Alaska-Siberian,  211. 

Bridgman,  P.  W.,  177,  224. 

Brooks,  W.  K.,  262. 

Brown,  E.  W.,  176,  224. 

Buffon,  65,  82. 

Cambrian    Period,  life-record    in, 

250. 

Capillary  soil  action,  254. 
Capillary  waters,  257;    reticulum 

of,  257. 
Capsules,  259. 

Captured  satellite,  earmarks  of,  1 53 . 
Carbides,  256,  257. 
Carbon  compounds,  243. 
Carbon  dioxide,  variation  in,  5. 
Caspio-Mediterranean  depressions , 

209,  218. 


263 


264 


THE  ORIGIN  OF  THE  EARTH 


Celestial  kinships,  101. 
Cell-filling,  259. 
Cell-inclosure,  260. 
Cellular  reticulum,  258. 
Centers  of  collection,  77,  79. 
Central  core,  240. 
Centrifugal  hypotheses,  43,  48,  55. 
Chain  of  syntheses,  244. 
Chamberlin,  R.  T.,  x. 

Chamberlin,  T.  C.,  37,  47,  71,  89, 
129,  158,  262;  and  Chamberlin, 
R.  T.,  262;  and  Salisbury,  R. 
D.,  158,  187,  262. 

Circularity  of  oceans,  198,  215,  219. 

Circularity  of  orbits,  150,  151. 

Circulation:  of  atmosphere,  195; 
of  ocean,  198. 

Circulatory  mechanism,  253. 

Circulator>'  system,  255. 

Close  approach,  101,  107. 

Coalescence  of  ocean  basins,  212. 

Collecting  centers,  77,  79;  knots, 
'33- 

Collection  of  ring  into  globe,  61. 

Collectors:  dynamic,  132;  physi- 
cal, 132". 

Collision,  glancing,  84. 

Collisional  atmosphere,  22. 

Collisional  hypothesis,  65. 

Collisional  zone,  20. 

Colloidal  state,  255. 

Colloid  chemico-physicist,  260. 

Colloids,  256,  259. 

Compressibility,  237. 

Cones,  sub-oceanic,  217,  218,  220, 
221;  evolution  of,  215. 

Configurations  of  earth,  greater, 
basal  features  of,  200. 

Conical  segments,  217. 

Contents,  xii. 

Contravening  agencies,  27. 

Control  of  temperature,  lique- 
f active,  239. 


Cook,  S.  R.,  37. 

Co-operation  of  lithosphere,  hy- 
drosphere, and  atmosphere,  168. 

Core,  central,  240. 

Cosmogonic  states,  significance  of 
vestiges  of,  38. 

Cosmogonic  views,  older,  64. 

Creation,  ex  nihilo,  63,  64. 

Criterion:  of  momentum,  41; 
supreme,  261. 

Critical  features  of  planetary  sys- 
tem, 68. 

Critical  velocity,  17,  18,  33;  erro- 
neous and  true,  15. 

Crystallization,  183;  and  depth, 
179. 

Crystalloids,  256,  259. 

Currents:  ascending,  248;  de- 
scending, 248. 

Curve,  thermal,  239. 

Darwin,  Sir  George,  45,  47,  53, 
54,  75,  89,  177,  178,  190,  224. 

Dedication,  vii. 

Depressions,  Caspio-Meditenra- 
nean,  209. 

Descending  currents,  248. 

Devil's  Post  Pile,  186. 

Discoidal  form  of  planetary  sys- 
tem, 69. 

Discrepancies  in  Laplacian  hy- 
pothesis, 43,  49. 

Dissociation,  35. 

Distortional  seismic  waves,  181. 

Divergent  courses  of  heat,  233. 

Dominance,  law  of,  221. 

Double  spiral  nebula,  156. 

Downward  changes,  zone  of, 
242. 

Dune  surface,  primitive,  billowy 
configuration  of,  249. 

Dust,  planetesimal,  248. 

Dynamic  encounter,  101. 

Dynamic  vestiges,  39,  41. 


INDEX 


265 


Early  biogenetic  conditions,  247. 

Earth:  autobiography  of,  38; 
equatorial  velocity  of,  42;  in- 
fantile, basis  of  growth  of,  191; 
juvenile,  inner  reorganization 
of,  226;  juvenile  shaping  of, 
159;  plane  of  orbit  of,  46. 

Earth-genesis,  gaseous  theory  of, 
in  light  of  kinetic  theory  of 
gases,  10. 

Earth-knot,  initial  rotation  of,  174. 

Earth-moon  ring,  stage  of,  50. 

East  Indian  view  of  globe,  210. 

East  Indies,  seismic  and  volcanic 
disturbances  in,  213. 

Eccentricities  of  orbits  of  plane- 
toids, 69. 

Elasticity  and  magnetism,  161. 

Electric  action,  29,  148. 

Electric  differentiations,  30. 

Embryonic  elements  of  configu- 
ration of  earth,  200. 

Embryonic  framework,  194,  203, 
204;  of  infantile  earth,  basis 
of  growth,  of,  19 1. 

Endothermic  arrangement,  240. 

Endothermic  reactions,  238. 

Equatorial  velocity:  of  earth,  42; 
of  parent  nebula,  42. 

Equilibrium  rate  of  rotation,  174. 

Equilibrium  rotation,  99. 

Eruptive  prominences  of  sun,  104, 
106,  109,  113,  154. 

Escape:  of  atmosphere,  compu- 
tation relative  to,  31;  of  lavas, 
231;  of  molecules,  31;  pro- 
gressional  mode  of  molecular, 
23;  progressive  orbital,  25; 
velocity  of,  24. 

Eurafrican  quadrilateral,  view  of, 
209. 

Eutectics,  235. 

Evolution:  of  satellites,  55;  of 
solar  nebula  into  planetary  sys- 
tem, 130;  of  sub-oceanic  cones, 
215;  vestiges  of,  58. 


Fingal's  Cave,  186. 

Fish-Mouth  Nebula,  86. 

Flexibility  of  West  Indies,  211. 

Forbidden  field,  90. 

Forelands,  254. 

Forward  rotation,  58,  90. 

Framework:  basal,  213;  modifi- 
cations of,  193;  primitive,  193, 
194,  203,  204. 

Fulcrum  zone,  188. 

Futile  efforts,  72. 

Gale,  H.  G.,  224. 

Gaseo-molten  genesis,  9. 

Gaseous  globe,  test  carried  back 
to,  34. 

Gaseous  hypothesis,  48. 

Gaseous  theory  of  earth-genesis 
in  light  of  kinetic  theory  of 
gases,  10. 

Gases:  distribution  of,  51;  old 
view  of,  10. 

Geo-naturalist,  31. 

Giant  nebula,  128. 

Giant  nebulae,  127. 

Giant's  Causeway,  186,  187. 

Glauert,  H.,  224. 

Globe:  Antillean  view  of,  207; 
East  Indian  view  of,  210;  Euraf- 
rican view  of,  209;  Indian 
Ocean  view  of,  216;  North 
Atlantic  view  of,  212;  North 
Pacific  view  of,  222;  South  At- 
lantic view  of,  206;  South  Pa- 
cific view  of,  219;  south-polar 
view  of,  205. 

Gradient,  thermal,  234. 

Granite  foundations,  8. 

Granitic  intrusions,  8. 

Great  contact  horizons,  higher 
organization  in,  241. 

Great  Nebula  in  Orion,  86. 

Great  world-ridge,  213. 

Growth  of  embryonic  framework 
of  infantile  earth,  basis  of,  191. 


266 


THE  ORIGIN  OF  THE  EARTH 


Grubenmann,  U.,  225. 
Gyral  systems,  196. 
Gyrals,  bi-zonal,  197. 

Hale,  G.  E.,  29. 

Hall,  A.,  56. 

Heat:  divergent  courses  of,  233; 
generation  of,  227. 

Heat  generators,  236. 

Heavy  rigid  factors,  219. 

Hecker,  191. 

Hemispheres,  contrasts  of,  201. 

Hexafid  earth,  189;  flexibility  of, 
191. 

Hexafid  segmentation,  213. 

Highs,  permanent,  196. 

Hydrosphere:  collection  of,  167; 
co-operation  with  lithosphere 
and  atmosphere,  168. 

Hydrospheric  influences,  modi- 
fying, 197. 

Hyperbolic  path,  16. 

Hypothesis:  centrifugal,  43,  48, 
55;  collisional,  65;  Kantian,  66, 
67;  Laplacian,  u,  19,32,41,49, 
61;  less  specific,  63,  64;  me- 
teoritic,  75;  planetesimal,  130- 
58. 

Imperfection  of  theoretical  series, 
244. 

Inclination  of  planetary  orbits, 
46. 

Independence  of  volcanoes,  231. 
Indian  Ocean  basin,  217. 
Indian  Ocean  view  of  globe,  216. 
Inelastic  aggregates,  160. 
Initial  biologic  habitat,  250. 
Inner   reorganization   of  juvenile 

earth,  226,  238. 
Inorganic  syntheses,  246. 
Inquiry:     along    collisional    lines, 

82;    along    gaseous    lines,    74; 

along  meteoritic  lines,  74. 
Interchange  of  atmospheres,  32. 


Interior:    stress  control  of,   228; 

temperature  and  physical  state 

of,  161. 

Internal  movement,  180. 
Introduction,  i. 
Intrusions,  granitic,  8. 
Irregularities:     of    Mercury    and 

Venus,  176;   of  moon,  176. 

Johnston,  John,  225. 

Jupiter,  42,  50,  52,  54,  55,  56,  135, 
T36»  I37>  153;  moons  of,  70. 

Juvenile  earth,  inner  reorgani- 
zation of,  226. 

Juvenile  shaping  of  earth,  159. 

Kantian  hypothesis,  66,  67. 
Katamorphism,  zone  of,  242. 
Kinetic  view:    of  gases,    n,   37; 

revisions  of,  32. 
Knots:  and  nebulous  haze,  nature 

of,  136;   collecting  centers,  133; 

cores  of,  142;  masses  of,  138. 
Krakatoan  atmosphere,  ultra,  248. 
Krenal    atmosphere,    20,    21,    22, 

157;  of  sun,  26. 
Krenal  zone,  20,  21. 

Land  hemisphere,  222. 

Laplace,  2,  10. 

Laplacian  hypothesis,  n,  61;  at- 
mospheric test  of,  32;  postu- 
lates of,  41;  specific  defects  of, 
49;  testing  tenets  of,  49. 

Larmor,  Sir  Joseph,  224. 

Lavas,  escape  of,  231. 

Law:  of  alternates,  221;  of 
dominance,  221;  of  opposites, 
221;  of  probabilities,  test  by, 
130. 

Leith,  C.  K.,  225. 

Less  specific  hypotheses,  63. 

Lick  Observatory,  80,  83,  119, 
121. 

Life,  maintenance  of,  261. 


INDEX 


267 


Life-genesis,  special  demands  of, 
252. 

Life-record  in  Cambrian  Period, 
250. 

Light-pressure,  27,  28. 

Lion  in  the  way,  78, .90. 

Liquefaction,  selective,  235,  238. 

Liquefactive  control  of  tempera- 
ture, 239. 

Lithosphere,  co-operation  with 
hydrosphere  and  atmosphere, 
168. 

Living  organisms,  appearance  of, 
244. 

Lunn,  A.  C.,  47. 

MacMillan,  W.  D.,  47. 

Magnetic  action,  148. 

Magnetism:  and  elasticity,  161; 
and  rotation,  160. 

Maintenance  of  life,  261. 

Mars,  56,  137,  138,  139,  142. 

Masses  and  momenta,  test  of,  52. 

Master- features,  215. 

Material  vestiges,  38. 

Maxwell,  Clerk-,  12,  14. 

McCoy,  H.  N.,  x. 

Mead,  W.  J.,  225. 

Mechanistic,  247,  262. 

Mercury,  42,  50,  137,  138,  139 
142;  irregularities  of,  176. 

Meridional  lines,  210. 

Meridional  trends,  207. 

Metallic  alloys,  240. 

Meteorites,  163;  plunge  of,  31. 

Meteoritic  hypothesis,  quasi- 
gaseous  form  of,  75. 

Methods  of  inquiry,  39. 

Michelson,  A.  A.,  191,  224. 

Mild-temperature  engine,  260. 

Modifications  of  framework,  193. 

Modifying  influences:  atmos- 
pheric, 193;  hydrospheric,  197. 

Molecular  activity,  12. 


Molecular  escape:  critical  velocity 
of,  33;  second  mode  of,  24. 

Molecular  velocities,  14,  33. 

Molecules:  escape  of,  31;  orbital, 
23;  paths  of,  19. 

Moment  of  momentum,  41. 

Momentum,  60;  in  nebula,  value 
of,  50;  moment  of,  41;  percent- 
age of,  70. 

Mono-parental  origin,  101. 

Moon:  irregularities  of,  176. 

Moons  of  Jupiter  and  Saturn,  70. 

Moulton,  E.  J.,  119. 

Moulton,  F.  R.,  x,  18,  33,  37,  47, 
49>  5o>  51*  56,  61,  71,  no,  in, 
119,  123,  129,155,  156,  158,  237. 

Mount  Wilson  Solar  Observatory, 
131.  156- 

Movement,  mode  of  internal,  182. 

Movements,  due  to  changes  of 
rotation,  184. 

Nebula:  giant,  127,  128;  testi- 
mony of,  124;  value  of  momen- 
tum of,  50; 

— solar:  evolution  of  into  plane- 
tary system,  130; 

—spiral:  117,  119,  121,  125,  131; 
assigned  modes  of  development 
of,  122;  two  arms  of,  124. 

Nebular  ring,  test  applied  to,  35. 

Nebulous,  haze  and  knots,  nature 
of,  136. 

Nebulous  matter,  aggregation  of, 
i45- 

Neptune,  42,  50,  135,  137,  152, 
153- 

Nolan,  56,  71. 

North  Atlantic  basin,  217. 

North    Atlantic    view    of    globe, 

212. 

North  Pacific  basin,  217. 
North  Pacific  quadrilateral,  211. 
North  Pacific  view  of  globe,  222. 
North-south  swaying  of  pyramids, 
190. 


268 


THE  ORIGIN  OF  THE  EARTH 


Oblique  rotation,  96. 

Ocean  basins,  coalescence  of,  212. 

Ocean  circulation,  198. 

Ocean,  primitive,  251. 

Oceanic  basins,  217. 

Oceans:  circularity  of,  198,  215, 
219;  paired,  213. 

Offset  positions,  214. 

Older  cosmogonic  views,  64. 

Open  reticulum,  258. 

Opposites,  law  of,  221. 

Orbital  atmosphere,  21,  22,  157; 
of  sun,  26. 

Orbital  molecules,  23. 

Orbital  movements,  momentum 
requisite  for,  60. 

Orbits:  assigned  mode  of  devel- 
oping of,  123;  circularity  of ,  149, 
150,  151; 

— of  planetoids,  55;  eccentricities 
of,  69. 

Organic  chemist,  260. 

Organization,  higher,  in  great  con- 
tact horizons,  241. 

Origin:  bi-parental,  101;  mono- 
parental,  101;  of  satellites  and 
satellitesimals,  143. 

Osmosis,  260. 

Osmotic  action,  255. 

Parabolic  velocity,  16,  33. 
Parallel  recrystallization,  240. 
Permanent  highs,  196. 
Phobos,  56. 

Physical  state  of  interior,  161. 
Plane  of  sun's  rotation,  130. 
Planetary  atmospheres,  31,  157. 
Planetary  control  of  gases,  13. 
Planetary  knots,  specific  features 

of,  132. 
Planetary   masses,  symmetry    of, 

54- 
Planetary   orbits,    inclination    of, 

46. 


Planetary  system:    a  closely  ap- 

pressed  disk,  68;    evolution  of 

solar  nebula  into,  130. 
Planetary  tides,  incompetency  of, 

45- 

Planetesimal  dust,  164,  165;  bur- 
den of,  248. 
Planetesimals,  142,  146,  147,  148; 

definition  of,  139. 
Planetoids,  birth  of,  135;    orbits 

of  55;    inclined  to  equator  of 

sun,  69. 
Planets:  atmospheres  of ,  26;  orbits 

of,  inclined  to  equator  of  sun, 

69;   spacing  of,  150. 
Preface,  ix. 

Primary  segmentation,  185. 
Primeval  chaos,  64. 
Primitive    framework,    193,    194, 

203,  204;  outgrowths  of,  203. 
Primitive  ocean,  251. 
Probabilities,  law  of,  test  by,  130. 
Prohibitive  ban,  90,  95. 
Psychic  action,  247. 
Psychological  element,  advent  of, 

246. 

Psychologist,  260. 
Pyramidal  segments,  217. 
Pyramids,  four-sided,  189. 

Quadrilateral :  North  Pacific,  211; 

of  Indian  Ocean,  216. 
Quadrilaterals,  189,  192,  206. 
Quasi-organic  syntheses,  242. 

Radioactive  factor,  227. 
Radioactive  particles,  31. 
Radioactivity,  236. 
Reactions,  endothermic,  238. 
Reciprocity,  atmospheric,  27. 
Recombination,  235. 
Records,  materialistic,  39. 
Recrystallization:     parallel,    240; 
rock-flow  by,  231. 


INDEX 


269 


References,   37,   47,   71,  89,    129, 

158,  224,  225,  262. 
Reorganization,  235;  inner,  238. 
Reticulum:  •     cellular,     258;      of 

capillary  waters,  257;  open,  258. 
Retrograde  rotation,  58,  59,  90. 
Retrograde  satellites,  56,  153. 
Rigid  factors,  heavy,  219. 
Ring  nebula,  83. 
Rings,  55,  57;    formation  of,  58; 

of  Saturn,  58,  59. 
Ring  theory,  57. 
Roche,  Eduard,  102,  129. 
Roche  limit,  136. 
Rock-flow,    182;     by    recrystalli- 

zation,  231. 

Rotating  bodies,  magnetic,  160. 

Rotation:  changes  of ,  175;  move- 
ment required  by,  184;  direction 
of,  70;  equilibrium  of,  99; 
equilibrium  rate,  174;  forward 
58,  90;  initial,  of  earth-knot, 
174;  oblique,  96;  rate  of,  41, 
retrograde,  58,  59,  90;  of  the 
sun,  134;  velocity  of,  43. 

Rotational  stress-differences,  229. 

Salisbury,  R.  D.,  and  Chamberlin, 
T.  C.,  158,  187. 

Satellite,  captured,  earmarks  of, 
153. 

Satellite  knots,  144,  155;  satel- 
lite rings,  55;  satellites:  and 
satellitesimals,  origin  of,  143; 
evolution  of,  55;  growth  and 
adjustment  of,  152;  retrograde, 
56,  153- 

Satellitesimal  matter,  165. 

Satellitesimals,  146,  147,  155; 
definition  of,  144;  origin  of 
satellites  and,  143. 

Saturn,  56,  135,  ^  136,  137,  153; 
moons  of,  70;  rings  of,  58,  59. 

Saw-tooth  arrangement  in  equa- 
torial belt,  189. 

Schistose  structure,  240. 


Schistosity,  183,  217. 

Scrope,  187. 

Secular  perpetuation  of  differences 
of  specific  gravity,  198. 

Seeding  new  ground,  260. 

Segmentation,  primary,  185. 

Segments:  sub-oceanic,  217;  tri- 
angular, 188,  189. 

Segregation  of  heavy  material, 
159. 

Seismic  disturbances,  in  East  and 
West  Indies,  213. 

Seismic  waves,  181;  distortional, 
181;  transmission  of ,  240. 

Selective  liquefaction,  235,  238. 

Selective  segregation  of  heavy  ma- 
terial, 159. 

Shaping  agencies,  172. 

Shorelands,  254. 

Slichter,  C.  S.,  47- 

Soil  action,  capillary,  254. 

Soil-breathing,  255. 

Soil-films,  258. 

Solar  eruptions,  103;  belt  of,  133, 

Solar  nebula,  130;  evolution  of, 
into  planetary  system,  130. 

Solar  prominences,  104. 

Solar  system,  decisive  testimony 
of  vestiges  of,  48. 

Solid-flow,  182. 

Solution-curve,  234. 

South  Atlantic,  217. 

South  Atlantic  view  of  globe, 
206. 

South  Pacific  basin,  217. 

South  Pacific  view  of  globe,  219. 

South-polar  view  of  globe,  205. 

Spacing  of  planets,  150. 

Specific  gravity:  high,  181;  secu- 
lar perpetuation  of  differences 
of,  198. 

Spectroscope,  59. 

Speculations,  subconscious,  73. 


270 


THE  ORIGIN  OF  THE  EARTH 


Sphere:  of  control,  18,  23;  of 
influence,  18. 

Spiral  nebula,  80,  81,  117,  119, 
121,  125,  131;  assigned  modes 
of  development  of,  122;  double, 
156;  two  arms  of ,  1 24. 

Spiritual,  247. 

Stieglitz,  J.,  47. 

Stoney,  G.  Johnstone,  20,  21,  32, 
33.  37- 

Stress-control  of  interior,  228. 

Stress-differences:  of  tides,  177, 
178;  rotational,  229. 

Stresses:  distribution  of,  177; 
tensional,  186. 

Sub-knots,  144. 

Sub-oceanic  cones,  217,  218,  220, 
221;  evolution  of,  215. 

Sub-oceanic  segments,  217. 

Sun:  effects  of  tides  in,  44;  elec- 
tric fields  of,  29;  eruptive  promi- 
nences of,  104,  106,  109,  113, 
154;  inclination  of  equator  of, 
69;  obliquity  of  axis  of,  41; 
plane  of  equator  of,  46;  present 
rotation  of,  41;  rotation  of, 
134;  plane  of  rotation,  130; 
ultra-atmosphere  of,  26,  27; 
vestiges  in,  40. 

Supplementary  agencies  acting  on 
atmosphere,  27. 

Supreme  criterion,  261. 

Swaying  of  pyramids,  north-south, 
190. 

Symmetry  in  planetary  masses, 
54- 

Syntheses:  chain  of,  244;  inor- 
ganic, 246;  quasi-organic,  242. 

Synthetic  compounds,  243. 

Temperature:  liquefactive  con- 
trol of,  239;  of  interior,  161. 

Tensional  stresses,  186. 

Terrestrial  planets,  knots  of,  142. 

Test:  applied  to  nebular  ring,  35; 
carried  back  to  gaseous  globe, 


34;  of  masses  and  momenta,  52; 

ultimate,  36. 
Theoretical  series,  imperfection  of, 

244. 

Thermal  curve,  239. 
Thermal  gradient,  234. 
Thomson,  J.  J.,  30. 
Tibetan  regions,  248. 
Tidal  action,  adaptation  to,  190. 
Tidal  cones,  in. 
Tidal  forces,  1 10. 
Tides:    in  sun,  effects  of,  44;    in- 

cojnpetency   of   planetary,   45; 

stress-differences  of,  177,  178. 
Titicacan  regions,  248. 
Transcendent,  262. 
Transcendent  and  transcendental 

features  of  earth's  evolution,  262. 
Transmission  of  seismic  waves,  240. 
Triangles,  pairs  of,  189. 
Trifid  segmentation,  213. 
Tyndall,  2,5. 

Ultra-atmosphere,  19,  21,  22,  27, 

59,  144- 
Ultra-atmospheres   of   earth   and 

sun,  equilibrium  of,  26,  27. 
Ultra-Krakatoan  atmosphere,  248. 
Undercooled  liquids,  181. 
Uranus,  135,  137,  153. 

Van  Hise,  C.  R.,  225. 

Venus,  137,  142;  irregularities  of, 
176. 

Velocity:  critical,  33;  from  infin- 
ity, 16;  of  escape,  24;  of  sun's 
equator,  43;  parabolic,  33. 

Vestiges:  dynamic,  39;  in  the 
sun,  40;  material,  38;  of  cos- 
mogonic  states  and  their  sig- 
nificance, 38;  of  evolution,  58; 
of  solar  system,  decisive  testi- 
mony of,  48. 

Volcanic  disturbances  in  East  and 
West  Indies,  213. 


INDEX 


271 


Volcanoes,  independence  of,  231. 
Volitional,  262. 
Vulcan,  42. 

Water-hemisphere,  222. 

Waters,  capillary,  257. 

Waves:  seismic,  181;  transmis- 
sion of,  240. 

Weak  factors,  light,  219. 

West  Indies:  flexibility  of,  211; 
seismic  and  volcanic  disturb- 
ances in,  213. 


Whitney,  A.  W.,  33,  37. 
Woodward,  R.  S.,  77. 

Yerkes  Observatory,  86,  104,  106, 
109,  117,  128,  143,  154. 

Yield-hemisphere,  204. 

Yield-tracts,  204,   206,  208,  210, 
213. 

Zone:  of  downward  changes,  242; 
of  katamorphism,  242. 


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The  Living  Cycads.     By  CHARLES  JOSEPH  CHAMBERLAIN. 
Mechanics  of  Delayed  Germination  in  Seeds.     By  W.  CROCKER. 
The  Rigidity  of  the  Earth  and  of  Materials.      By  A.  A.  MlCHELSON. 
The  Problem  of  Fertilization.     By  FRANK  R.  LiLLlE. 

Linear  Integral  Equations   in  General  Analysis.      By   ELIAKIM   HASTINGS 
MOORE. 

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